@article{25951, abstract = {{Nanoporous Materials, like carbons, silica and semiconducting metal oxides, play a major role in recent scientific research, especially in the fields of energy storage, catalysis, material separation and sensor technology. Thus, our aim is to focus on simple synthesis concepts for these materials, such as soft matter templating or nanocasting, which can be easily introduced by means of appropriate models in school chemistry education or school laboratories. In addition to facile and realizable syntheses in school, several experiments concerning catalysis and gas sensing will be presented, too. By these experiments the characteristics of nanoporous materials can be obviously demonstrated and additionally, these experiments can serve as a starting point for further experiments that could easily be developed by students themselves, particularly in relation to environmental issues.}}, author = {{Wilke, Timm and Haffer, Stefanie and Weinberger, Christian and Tiemann, Michael and Wagner, Thorsten and Waitz, Thomas}}, issn = {{1936-7449}}, journal = {{Journal of Nano Education}}, pages = {{117--123}}, title = {{{Nanoporous Materials: Synthesis Concepts and Model Experiments for School Chemistry Education}}}, doi = {{10.1166/jne.2014.1044}}, year = {{2014}}, } @article{25947, abstract = {{Ordered mesoporous carbon with a high heteroatom (N, O) content was prepared by nanocasting from a melt of a eutectic mixture of fructose and urea (60/40 wt.-%; melting temperature ca. 65 °C). These precursor compounds are cheap and environmentally friendly. The material possesses enhanced pore-wall surface polarity as compared to that of mesoporous carbon prepared by the same technique without urea. This was verified by water sorption analysis. As a result, the heteroatom-modified material shows higher sorption capacity for the uptake of heavy metal ions (Cu2+) from aqueous solution, which may be interesting for potential application in wastewater cleaning.}}, author = {{Weinberger, Christian and Haffer, Stefanie and Wagner, Thorsten and Tiemann, Michael}}, issn = {{1434-1948}}, journal = {{European Journal of Inorganic Chemistry}}, pages = {{2787--2792}}, title = {{{Fructose and Urea as Precursors for N-/O-Modified Mesoporous Carbon with Enhanced Sorption Capacity for Heavy Metal Ions}}}, doi = {{10.1002/ejic.201402027}}, year = {{2014}}, } @article{25954, abstract = {{The light-enhanced NO2 sensing behavior of mesoporous In2O3 is measured and interpreted by means of a new sensing model. The model aims at explaining (i) the drop in electronic resistance of n-type semiconducting In2O3 under UV light exposure, (ii) the light-enhanced reaction to oxidizing gases, and (iii) the faster reaction and regeneration in mesoporous In2O3 as compared to non-porous material. Contrary to the conventional double Schottky model the dominating factor for the change in resistance is a change of oxygen vacancy donor states (0.18 eV below the conduction band) in the bulk phase due to photoreduction, instead of chemisorption. For the faster reaction and regeneration we propose an explanation based on enhanced oxygen diffusion in the In2O3 crystal lattice, specifically dominant in the mesoporous structure. The response of ordered mesoporous In2O3 to NO2 is stronger than in case of unstructured bulk material (with an average grain size of ca. 40 nm). The reaction is significantly accelerated by illuminating the samples with UV light. However, the response of the mesoporous material is weaker in the illuminated case.}}, author = {{Wagner, Thorsten and Kohl, Claus-Dieter and Malagù, Cesare and Donato, Nicola and Latino, Mariangela and Neri, Giovanni and Tiemann, Michael}}, issn = {{0925-4005}}, journal = {{Sensors and Actuators B: Chemical}}, pages = {{488--494}}, title = {{{UV light-enhanced NO2 sensing by mesoporous In2O3: Interpretation of results by a new sensing model}}}, doi = {{10.1016/j.snb.2013.02.025}}, year = {{2013}}, } @article{25953, abstract = {{Nanostructure-related magnetic properties are investigated systematically for various mesoporous cobalt oxide (Co3O4) and cobalt ferrite (CoFe2O4) spinel phases. Synthesis of the materials by nanocasting offers the opportunity to obtain materials which are different from each other with respect to both specific surface area and crystallite size. As a result, the respective contributions of two types of interfaces, namely, “solid–gas” and “solid–solid” interfaces, to the magnetic ordering can be distinguished. Structural characterization of the porous materials by X-ray diffraction, N2 physisorption, and electron microscopy as well as investigation of the magnetic behavior (field-dependent magnetization and temperature-dependent susceptibility) are presented.}}, author = {{Haffer, Stefanie and Walther, Till and Köferstein, Roberto and Ebbinghaus, Stefan G. and Tiemann, Michael}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, pages = {{24471--24478}}, title = {{{Nanostructure-Related Magnetic Properties of Various Mesoporous Cobalt Oxide and Cobalt Ferrite Spinel Phases}}}, doi = {{10.1021/jp409058t}}, year = {{2013}}, } @article{25952, abstract = {{Ordered mesoporous materials have great potential in the field of gas sensing. Today various template-assisted synthesis methods facilitate the preparation of silica (SiO2) as well as numerous metal oxides with well-defined, uniform and regular pore systems. The unique nanostructural properties of such materials are particularly useful for their application as active layers in gas sensors based on various operating principles, such as capacitive, resistive, or optical sensing. This review summarizes the basic aspects of materials synthesis, discusses some structural properties relevant in gas sensing, and gives an overview of the literature on ordered mesoporous gas sensors.}}, author = {{Wagner, Thorsten and Haffer, Stefanie and Weinberger, Christian and Klaus, Dominik and Tiemann, Michael}}, issn = {{0306-0012}}, journal = {{Chem. Soc. Rev.}}, pages = {{4036--4053}}, title = {{{Mesoporous materials as gas sensors}}}, doi = {{10.1039/c2cs35379b}}, year = {{2013}}, } @inproceedings{54994, author = {{Wagner, Thorsten and Tiemann, Michael and Kohl, Claus-Dieter and Morandi, Sara and Malagù, Cesare and Donato, Nicola and Latino, Mariangela and Neri, Giovanni}}, booktitle = {{Proceedings IMCS 2012}}, publisher = {{AMA Service GmbH, Von-Münchhausen-Str. 49, 31515 Wunstorf, Germany}}, title = {{{Mechanistic Model for UV light-enhanced NO2 Sensing utilizing Ordered Mesoporous In2O3}}}, doi = {{10.5162/imcs2012/p1.3.17}}, year = {{2012}}, } @inproceedings{54995, author = {{Klaus, Dominik and Tiemann, Michael and Wagner, Thorsten}}, booktitle = {{Proceedings IMCS 2012}}, publisher = {{AMA Service GmbH, Von-Münchhausen-Str. 49, 31515 Wunstorf, Germany}}, title = {{{Nanostructured Metal Oxides for High-Temperature Gas Sensing: Structural Stabilization in Porous Metal Oxides}}}, doi = {{10.5162/imcs2012/p2.0.3}}, year = {{2012}}, } @inbook{25960, abstract = {{We report on sensing properties of ordered mesoporous nanostructures of In2O3 synthesized by nanocasting procedure towards NO2. The nanostructured material shows improved recover times and higher responses compared to non nanostructured material at low operating temperatures (100–150°C) thus allowing the use for low power NO2 sensors. These properties may be related to fast oxygen in and out propagation facilitated by an enhanced surface accessibility of the nanostructure.}}, author = {{Donato, Nicola and Wagner, Thorsten and Tiemann, Michael and Waitz, Thomas and Kohl, Claus-Dieter and Latino, Mariangela and Neri, Giovanni and Spadaro, Donatella and Malagù, Cesare}}, booktitle = {{Lecture Notes in Electrical Engineering}}, issn = {{1876-1100}}, title = {{{NO2 Sensors with Reduced Power Consumption Based on Mesoporous Indium Oxide}}}, doi = {{10.1007/978-1-4614-0935-9_10}}, year = {{2012}}, } @article{25956, abstract = {{A model is proposed for the drop in electronic resistance of n-type semiconducting indium oxide (In2O3) upon illumination with light (350 nm, 3.5 eV) as well as for the (light-enhanced) sensitivity of In2O3 to oxidizing gases. Essential features of the model are photoreduction and a rate-limiting oxygen-diffusion step. Ordered, mesoporous In2O3 with a high specific surface area serves as a versatile system for experimental studies. Analytical techniques comprise conductivity measurements under a controlled atmosphere (synthetic air, pure N2) and temperature-resolved in-situ Fourier transform infrared (FTIR) spectroscopy. IR measurements reveal that oxygen vacancies form a donor level 0.18 eV below the conduction band.}}, author = {{Wagner, Thorsten and Kohl, Claus-Dieter and Morandi, Sara and Malagù, Cesare and Donato, Nicola and Latino, Mariangela and Neri, Giovanni and Tiemann, Michael}}, issn = {{0947-6539}}, journal = {{Chemistry - A European Journal}}, pages = {{8216--8223}}, title = {{{Photoreduction of Mesoporous In2O3: Mechanistic Model and Utility in Gas Sensing}}}, doi = {{10.1002/chem.201103905}}, year = {{2012}}, } @article{25957, abstract = {{Poröse Funktionsmaterialien wie halbleitende Metalloxide, Kohlenstoff-Formen oder auch Silica werden aktuell von verschiedenen Wissenschaftsdisziplinen intensiv für Bereiche der Energiespeicherung, Sensorik, Katalyse und Stofftrennung erforscht. Im Beitrag werden schwerpunktmäßig geordnet-mesoporöse Silica-Materialien behandelt, die seit etwa 20 Jahren synthetisch zugänglich sind. Neben den Grundlagen der Herstellung über ein Templat-Verfahren werden im Beitrag auch drei Experimente vorgestellt, die im Chemieunterricht oder Schülerlabor durchgeführt werden können. Zudem wird gezeigt, dass sich verschiedene Aspekte aus dem Kompetenzbereich Fachwissen mit Hilfe des Themas „Mesoporöse Silica“ miteinander vernetzen lassen.}}, author = {{Wilke, Timm and Haffer, Stefanie and Tiemann, Michael and Waitz, Thomas}}, issn = {{0944-5846}}, journal = {{CHEMKON}}, pages = {{67--72}}, title = {{{Mesoporöse Silica - Moderne Funktionsmaterialien im Chemieunterricht}}}, doi = {{10.1002/ckon.201210170}}, year = {{2012}}, } @article{25955, abstract = {{Crystalline, mesoporous alumina (Al2O3) materials with specific surface areas up to 400 m2 g–1 have been synthesized by means of structure replication (nanocasting) using CMK-8 carbon as a structure matrix. A crucial step during this synthesis procedure is the conversion of aluminum nitrate into aluminum hydroxide by treatment with ammonia vapor. The impact of this step was investigated in some detail. Prolonged vapor treatment has a positive impact on the crystallinity of the final Al2O3 products but at the same time leads to loss of mesoscopic structural order and porosity.}}, author = {{Haffer, Stefanie and Weinberger, Christian and Tiemann, Michael}}, issn = {{1434-1948}}, journal = {{European Journal of Inorganic Chemistry}}, pages = {{3283--3288}}, title = {{{Mesoporous Al2O3 by Nanocasting: Relationship between Crystallinity and Mesoscopic Order}}}, doi = {{10.1002/ejic.201200131}}, year = {{2012}}, } @article{25965, abstract = {{Nanoporous ZnO powders with high surface-to-mass ratios (SMR) between 15 and 70 m2 g−1 are synthesized, structurally characterized, and studied by time-resolved photoluminescence (PL). A strong dependence of the recombination dynamics and spectral width on SMR is observed at T = 10 K, and pronounced disorder-induced effects are found in the temperature dependence. Both the thermally induced shift of the PL maximum and the spectrally integrated PL intensity are interpreted by appropriate theoretical models. This consistent quantitative analysis of the experimental data yields a characteristic energy of 15 meV for the disorder scale in the nanoporous ZnO sample with an intermediate SMR.}}, author = {{Chernikov, Alexej and Horst, Swantje and Waitz, Thomas and Tiemann, Michael and Chatterjee, Sangam}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, pages = {{1375--1379}}, title = {{{Photoluminescence Properties of Ordered Mesoporous ZnO}}}, doi = {{10.1021/jp104293e}}, year = {{2011}}, } @article{25962, abstract = {{We report the correlation of the aging of Pd-doped SnO2 methane sensors with the change of the oxidation state of Pd. Mesoporous SnO2 doped with palladium species was prepared and exposed to different gas mixtures at high temperature (600 °C) to simulate long term usage. After each exposure step a fraction of the sample was cooled down to “freeze” the current oxidation state of Pd which was then analyzed by X-ray Absorption Near-Edge Spectroscopy (XANES) using the 'white line' (i.e. the absorption peak corresponding to the transition from the 2p3/2 core level to unoccupied 4 d states) intensity of the L(III) edge as a probe for the oxidation state. The Pd oxidation state correlates with the response of the resistive SnO2 sensor to methane gas, as determined by measuring the gas response to different concentrations of methane. Samples treated with 5000 ppm methane in air show a significant reduction of Pd(II) to Pd(0), depending clearly on the carrier gas (synthetic air, pure nitrogen) and on the temperature (600 °C vs. 300 °C).}}, author = {{Wagner, T. and Bauer, M. and Sauerwald, T. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0040-6090}}, journal = {{Thin Solid Films}}, pages = {{909--912}}, title = {{{X-ray absorption near-edge spectroscopy investigation of the oxidation state of Pd species in nanoporous SnO2 gas sensors for methane detection}}}, doi = {{10.1016/j.tsf.2011.04.187}}, year = {{2011}}, } @article{25964, abstract = {{Capacitive sensors are the most commonly used devices for the detection of humidity because they are inexpensive and the detection mechanism is very specific for humidity. However, especially for industrial processes, there is a lack of dielectrics that are stable at high temperature (>200 °C) and under harsh conditions. We present a capacitive sensor based on mesoporous silica as the dielectric in a simple sensor design based on pressed silica pellets. Investigation of the structural stability of the porous silica under simulated operating conditions as well as the influence of the pellet production will be shown. Impedance measurements demonstrate the utility of the sensor at both low (90 °C) and high (up to 210 °C) operating temperatures.}}, author = {{Wagner, Thorsten and Krotzky, Sören and Weiß, Alexander and Sauerwald, Tilman and Kohl, Claus-Dieter and Roggenbuck, Jan and Tiemann, Michael}}, issn = {{1424-8220}}, journal = {{Sensors}}, pages = {{3135--3144}}, title = {{{A High Temperature Capacitive Humidity Sensor Based on Mesoporous Silica}}}, doi = {{10.3390/s110303135}}, year = {{2011}}, } @article{25963, abstract = {{We report the synthesis of mesoporous tin dioxide (SnO2) materials with well-defined particle morphology. The products consist of uniform spheres with a diameter of 5 μm. The spheres are hierarchically porous with two distinct pore modes of 5.0 nm and 52 nm, respectively. This special porosity is the result of a synthesis procedure which involves a ‘hard templating’ (nanocasting) process. The product forms an approximately homogeneous monolayer of spheres on a sensor substrate and shows promising response to methane gas with low cross-sensitivity to water. The structural properties and gas-sensing performance are compared with a mesoporous SnO2 material without defined morphology, prepared by a ‘soft templating’ procedure.}}, author = {{Smått, J.-H. and Lindén, M. and Wagner, T. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0925-4005}}, journal = {{Sensors and Actuators B: Chemical}}, pages = {{483--488}}, title = {{{Micrometer-sized nanoporous tin dioxide spheres for gas sensing}}}, doi = {{10.1016/j.snb.2010.12.051}}, year = {{2011}}, } @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}}, }