@article{25961, abstract = {{Mesoporous In2O3, synthesized by a nanocasting procedure, is used as a resistive gas sensor for ozone in very low concentrations (from 20 ppb to 2.4 ppm) at room temperature. Its sensing performance is substantially increased by illumination with blue light (460 nm, 2.7 eV). For low ozone concentrations the sensor response increases with increasing humidity. However, higher humidity also results in the occurrence of a saturation of the response at lower ozone concentrations; this is rationalized by assuming a poisoning of surface active sites by hydroxyl groups.}}, author = {{Wagner, T. and Hennemann, J. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0040-6090}}, journal = {{Thin Solid Films}}, pages = {{918--921}}, title = {{{Photocatalytic ozone sensor based on mesoporous indium oxide: Influence of the relative humidity on the sensing performance}}}, doi = {{10.1016/j.tsf.2011.04.181}}, year = {{2011}}, } @article{25971, abstract = {{Precipitation of zinc sulfide particles is a very rapid process, and monitoring of the particle growth is experimentally very demanding. Applying a liquid jet flow cell, we were able to follow zinc sulfide particle formation on time scales down to 10−5 s. The flow cell was designed in such a way that data acquisition on the microsecond time scale was possible under steady-state conditions along a liquid jet (tubular reactor concept), allowing SAXS data accumulation over a time scale of minutes. We were able to monitor the growth of zinc sulfide particles and found experimental evidence for very rapid particle aggregation processes within the liquid jet. Under the experimental conditions the particle growth is controlled by mass transfer: i.e., the diffusion of the hydrogen sulfide into the liquid jet.}}, author = {{Schmidt, Wolfgang and Bussian, Patrick and Lindén, Mika and Amenitsch, Heinz and Agren, Patrik and Tiemann, Michael and Schüth, Ferdi}}, issn = {{0002-7863}}, journal = {{Journal of the American Chemical Society}}, pages = {{6822--6826}}, title = {{{Accessing Ultrashort Reaction Times in Particle Formation with SAXS Experiments: ZnS Precipitation on the Microsecond Time Scale}}}, doi = {{10.1021/ja101519z}}, year = {{2010}}, } @article{25967, abstract = {{We report the structural characterization and gas sensing properties of mesoporous SnO2 synthesized by structure replication (nanocasting) from ordered mesoporous KIT-6 silica. The products show a high thermal stability with no structural loss up to 600 °C and only minor decrease in specific surface area by 18% at 800 °C, as proven by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and nitrogen physisorption. In particular, the samples turn out to be much more stable than porous SnO2 materials prepared by sol–gel-based synthesis procedures for comparison. The thermal stability facilitates the utilization of the materials as sensors for combustible gases which react at high temperatures; test measurements reveal promising responses to methane (CH4) as an example.}}, author = {{Waitz, T. and Becker, B. and Wagner, T. and Sauerwald, T. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0925-4005}}, journal = {{Sensors and Actuators B: Chemical}}, pages = {{788--793}}, title = {{{Ordered nanoporous SnO2 gas sensors with high thermal stability}}}, doi = {{10.1016/j.snb.2010.08.001}}, year = {{2010}}, } @article{25972, abstract = {{In2O3 with ordered, uniform mesoporosity is prepared by nanocasting, using various porous silica phases (KIT-6, SBA-15) as structure matrices. The In2O3 particles exhibit well-defined morphologies (spherical or ellipsoidal, depending on the choice of silica matrix) and quite uniform sizes in the range of a few hundred nanometers. The regular morphology of the In2O3 particles is not associated with the morphological properties of the silica matrices. Instead, it is the result of the growth mechanism of In2O3 inside the silica pores; this mechanism is investigated in some detail. Hence, the nanocasting method offers a versatile and simple way of creating mesoporous In2O3 with regular morphology; this will be beneficial for many applications that require well-defined morphological properties, such as gas sensing or catalysis.}}, author = {{Haffer, Stefanie and Waitz, Thomas and Tiemann, Michael}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, pages = {{2075--2081}}, title = {{{Mesoporous In2O3 with Regular Morphology by Nanocasting: A Simple Relation between Defined Particle Shape and Growth Mechanism}}}, doi = {{10.1021/jp910336f}}, year = {{2010}}, } @article{25968, abstract = {{We report the synthesis of monodisperse, spherical periodic mesoporous organosilica (PMO) materials. The particles have diameters between about 350 and 550 nm. They exhibit a regular core-shell structure with a solid, non-porous silica core and a mesoporous PMO shell with a thickness of approximately 75 nm and uniform pores of about 1.7 nm. The synthesis of the core and the shell is carried out in a one-pot, two-stage synthesis and can be accomplished at temperatures between 25 and 100 °C. Higher synthesis temperatures lead to substantial shrinking of the solid core, generating an empty void between core and shell. This leads to interesting cavitation phenomena in the nitrogen physisorption analysis at 77.4 K.}}, author = {{Haffer, Stefanie and Tiemann, Michael and Fröba, Michael}}, issn = {{0947-6539}}, journal = {{Chemistry - A European Journal}}, pages = {{10447--10452}}, title = {{{Periodic Mesoporous Organosilica (PMO) Materials with Uniform Spherical Core-Shell Structure}}}, doi = {{10.1002/chem.201000643}}, year = {{2010}}, } @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}}, }