@article{25946, abstract = {{The synthesis of a periodically ordered, nanostructured composite consisting of CoFe2O4 and BaTiO3 is presented. In a first step, mesoporous CoFe2O4 is prepared by the structure replication method (nanocasting) using mesoporous KIT-6 silica as a structural mold. Subsequently, BaTiO3 is created inside the pores of CoFe2O4 by the citrate route, resulting in a well-ordered composite material of both phases. The two components are known for their distinct ferroic properties, namely ferrimagnetism (CoFe2O4) and ferroelectricity (BaTiO3), respectively. Therefore, this proof of synthesis concept offers new perspectives in the fabrication of composite materials with multiferroic properties.}}, author = {{Haffer, Stefanie and Lüder, Christian and Walther, Till and Köferstein, Roberto and Ebbinghaus, Stefan G. and Tiemann, Michael}}, issn = {{1387-1811}}, journal = {{Microporous and Mesoporous Materials}}, pages = {{300--304}}, title = {{{A synthesis concept for a nanostructured CoFe2O4/BaTiO3 composite: Towards multiferroics}}}, doi = {{10.1016/j.micromeso.2014.05.023}}, year = {{2014}}, } @article{25948, abstract = {{Ordered mesoporous silica phases (e.g. KIT-6, SBA-15) are used as structure matrices for negative replica structures of mesoporous In2O3. We present a detailed study on how the controlled synthesis of mono-, bi- and trimodal pore systems in the products is accomplished by systematic variation of the procedure of infiltrating a precursor species (In(NO3)3) into the pores of the silica matrix and subsequent thermal conversion into In2O3. Melt impregnation and conversion in a closed reactor facilitates a one-step casting process for ordered mesoporous indium oxide (In2O3). We present a model based on variation of the pore filling.}}, author = {{Klaus, Dominik and Amrehn, Sabrina and Tiemann, Michael and Wagner, Thorsten}}, issn = {{1387-1811}}, journal = {{Microporous and Mesoporous Materials}}, pages = {{133--139}}, title = {{{One-step synthesis of multi-modal pore systems in mesoporous In2O3: A detailed study}}}, doi = {{10.1016/j.micromeso.2014.01.007}}, year = {{2014}}, } @inbook{25944, abstract = {{Recently indium oxide (In2O3) attracted attention as a material for sensing layers in semiconducting gas sensors. Compared to frequently investigated materials like tin dioxide (SnO2), tungsten trioxide (WO3), or gallium oxide (Ga2O3) indium oxide offers some unique properties. The most prominent one is its selectivity to oxidizing gases such as ozone (O3) or nitrogen dioxide (NO2) at low operating temperatures (<150°C). Combined with the photoreduction properties of nanocast, porous In2O3 highly selective sensing layers with a fast response can be prepared. In some cases even room temperature measurements are possible; therefore this material allows for designing low-power sensors without the need for special sensor substrates (e.g., μ-hotplates). Detailed analysis of the sensing mechanism reveals that known sensing models are not able to describe the observed effects. Therefore a new sensing model for ordered nanoporous In2O3 is presented which will be applicable for nonstructured material too.}}, author = {{Wagner, Thorsten and Donato, Nicola and Tiemann, Michael}}, booktitle = {{Springer Series on Chemical Sensors and Biosensors}}, issn = {{1612-7617}}, title = {{{New Sensing Model of (Mesoporous) In2O3}}}, doi = {{10.1007/5346_2013_57}}, year = {{2014}}, } @inbook{25950, abstract = {{In this paper, the development and validation of a shield prototype for resistive sensor array characterization with Arduino UNO, a platform based on ATmega328 microcontroller provided by ATMEL, is reported. The resistance variation of the sensor can be evaluated by properly choosing the capacitance value and by measuring the period (frequency) of a custom inverter-based oscillator. The GUI and the developed firmware are able to perform the real-time monitoring of the sensor responses. The developed shield is able to measure the response of up to six sensors under UV radiation by means of LED devices. First results carried out with resistive sensors based on mesoporous In2O3-based material under UV light exposure are reported.}}, author = {{Aloisio, D. and Donato, N. and Neri, G. and Latino, M. and Wagner, T. and Tiemann, Michael and Capra, P. P.}}, booktitle = {{Lecture Notes in Electrical Engineering}}, issn = {{1876-1100}}, title = {{{Arduino-Based Shield for Resistive Gas Sensor Array Characterization Under UV Light Exposure}}}, doi = {{10.1007/978-3-319-00684-0_79}}, year = {{2014}}, } @inbook{25949, abstract = {{Due to their unique properties, ordered mesoporous carbon (OMC) materials prepared by nanocasting have raised great attention in recent years. Their synthesis usually comprises multiple cycles of impregnating a porous structure matrix with an aqueous solution of a suitable precursor, such as sucrose or other, often hazardous, compound. We present a more straightforward variation of this method by using fructose as the precursor compound. By using a solvent-free melt of the precursor, the impregnation requires only a single step. After carbonization by thermal decomposition and removal of the mesoporous silica structure matrix (SBA-15), ordered mesoporous carbon with one (CMK-3) or two (CMK-5) pore modes in two-dimensional, hexagonal symmetry (p6mm) is obtained.}}, author = {{Weinberger, Christian and Haffer, S. and Wagner, T. and Tiemann, Michael}}, booktitle = {{ACS Symposium Series}}, issn = {{0097-6156}}, title = {{{Fructose as a Precursor for Mesoporous Carbon: Straightforward Solvent-Free Synthesis by Nanocasting}}}, doi = {{10.1021/bk-2014-1183.ch001}}, year = {{2014}}, } @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}}, }