@article{25892, abstract = {{The tetratopic linker 1,1,2,2-tetrakis(4-phosphonophenyl)ethylene (H8TPPE) was used to synthesize the three new porous metal–organic frameworks of composition [M2(H2O)2(H2TPPE)]·xH2O (M = Al3+, Ga3+, Fe3+), denoted as M-CAU-53 under hydrothermal reaction conditions, using the corresponding metal nitrates as starting materials. The crystal structures of the compounds were determined ab initio from powder X-ray diffraction data, revealing small structural differences. Proton conductivity measurements were carried out, indicating different conductivity mechanisms. The differences in proton conductivity could be linked to the individual structures. In addition, a thorough characterization via thermogravimetry, elemental analysis, IR-spectroscopy as well as N2- and H2O-sorption is given.}}, author = {{Steinke, Felix and Javed, Ali and Wöhlbrandt, Stephan and Tiemann, Michael and Stock, Norbert}}, issn = {{1477-9226}}, journal = {{Dalton Transactions}}, pages = {{13572--13579}}, title = {{{New isoreticular phosphonate MOFs based on a tetratopic linker}}}, doi = {{10.1039/d1dt02610k}}, year = {{2021}}, } @article{25901, abstract = {{Thermally stabilized and subsequently carbonized nanofibers are a promising material for many technical applications in fields such as tissue engineering or energy storage. They can be obtained from a variety of different polymer precursors via electrospinning. While some methods have been tested for post-carbonization doping of nanofibers with the desired ingredients, very little is known about carbonization of blend nanofibers from two or more polymeric precursors. In this paper, we report on the preparation, thermal treatment and resulting properties of poly(acrylonitrile) (PAN)/poly(vinylidene fluoride) (PVDF) blend nanofibers produced by wire-based electrospinning of binary polymer solutions. Using a wide variety of spectroscopic, microscopic and thermal characterization methods, the chemical and morphological transition during oxidative stabilization (280 °C) and incipient carbonization (500 °C) was thoroughly investigated. Both PAN and PVDF precursor polymers were detected and analyzed qualitatively and quantitatively during all stages of thermal treatment. Compared to pure PAN nanofibers, the blend nanofibers showed increased fiber diameters, strong reduction of undesired morphological changes during oxidative stabilization and increased conductivity after carbonization.}}, author = {{Wortmann, Martin and Frese, Natalie and Mamun, Al and Trabelsi, Marah and Keil, Waldemar and Büker, Björn and Javed, Ali and Tiemann, Michael and Moritzer, Elmar and Ehrmann, Andrea and Hütten, Andreas and Schmidt, Claudia and Gölzhäuser, Armin and Hüsgen, Bruno and Sabantina, Lilia}}, issn = {{2079-4991}}, journal = {{Nanomaterials}}, title = {{{Chemical and Morphological Transition of Poly(acrylonitrile)/Poly(vinylidene Fluoride) Blend Nanofibers during Oxidative Stabilization and Incipient Carbonization}}}, doi = {{10.3390/nano10061210}}, year = {{2020}}, } @article{25899, abstract = {{Large Co-MOF-74 crystals of a few hundred micrometers were prepared by solvothermal synthesis, and their structure and morphology were characterized by scanning electron microscopy (SEM), IR, and Raman spectroscopy. The hydrothermal stability of the material up to 60 °C at 93% relative humidity was verified by temperature-dependent XRD. Proton conductivity was studied by impedance spectroscopy, using a single crystal. By varying the relative humidity (70–95%), temperature (21–60 °C), and orientation of the crystal relative to the electrical potential, it was found that proton conduction occurs predominantly through the linear, unidirectional (1D) micropore channels of Co-MOF-74, and that water molecules inside the channels are responsible for the proton mobility by a Grotthuss-type mechanism.}}, author = {{Javed, Ali and Strauss, Ina and Bunzen, Hana and Caro, Jürgen and Tiemann, Michael}}, issn = {{2079-4991}}, journal = {{Nanomaterials}}, title = {{{Humidity-Mediated Anisotropic Proton Conductivity through the 1D Channels of Co-MOF-74}}}, doi = {{10.3390/nano10071263}}, year = {{2020}}, } @article{25903, abstract = {{Porous tin dioxide is an important low-cost semiconductor applied in electronics, gas sensors, and biosensors. Here, we present a versatile template-assisted synthesis of nanostructured tin dioxide thin films using cellulose nanocrystals (CNCs). We demonstrate that the structural features of CNC-templated tin dioxide films strongly depend on the precursor composition. The precursor properties were studied by using low-temperature nuclear magnetic resonance spectroscopy of tin tetrachloride in solution. We demonstrate that it is possible to optimize the precursor conditions to obtain homogeneous precursor mixtures and therefore highly porous thin films with pore dimensions in the range of 10–20 nm (ABET = 46–64 m2 g–1, measured on powder). Finally, by exploiting the high surface area of the material, we developed a resistive gas sensor based on CNC-templated tin dioxide. The sensor shows high sensitivity to carbon monoxide (CO) in ppm concentrations and low cross-sensitivity to humidity. Most importantly, the sensing kinetics are remarkably fast; both the response to the analyte gas and the signal decay after gas exposure occur within a few seconds, faster than in standard SnO2-based CO sensors. This is attributed to the high gas accessibility of the very thin porous film.}}, author = {{Ivanova, Alesja and Frka-Petesic, Bruno and Paul, Andrej and Wagner, Thorsten and Jumabekov, Askhat N. and Vilk, Yury and Weber, Johannes and Schmedt auf der Günne, Jörn and Vignolini, Silvia and Tiemann, Michael and Fattakhova-Rohlfing, Dina and Bein, Thomas}}, issn = {{1944-8244}}, journal = {{ACS Applied Materials & Interfaces}}, pages = {{12639--12647}}, title = {{{Cellulose Nanocrystal-Templated Tin Dioxide Thin Films for Gas Sensing}}}, doi = {{10.1021/acsami.9b11891}}, year = {{2020}}, } @article{23854, abstract = {{Micropatterned nanoporous aluminum oxide arrays are prepared on silicon wafer substrates by using photopolymerized poly(dimethylacrylamide) hydrogels as porogenic matrices. Hydrogel micropatterns are fabricated by spreading the prepolymer mixture on the substrate, followed by UV photopolymerization through a micropatterned mask. The hydrogel is covalently bonded to the substrate surface. Al2O3 is produced by swelling the hydrogel in a saturated aluminum nitrate solution and subsequent thermal conversion/calcination. As a result, micropatterned porous Al2O3 microdots with heights in µm range and large specific surface areas up to 274 m2 g−1 are obtained. Hence, the hydrogel fulfills a dual templating function, namely micropatterning and nanoporosity generation. The impact of varying the photopolymerization time on the properties of the products is studied. Samples are characterized by light and confocal laser scanning microscopy, scanning electron microscopy, energy-dispersive x-ray spectrometry, and Kr physisorption analysis.}}, author = {{Chen, Zimei and Kuckling, Dirk and Tiemann, Michael}}, issn = {{0957-4484}}, journal = {{Nanotechnology}}, publisher = {{IOP Publishing}}, title = {{{Nanoporous aluminum oxide micropatterns prepared by hydrogel templating}}}, doi = {{10.1088/1361-6528/aba710}}, volume = {{31}}, year = {{2020}}, } @article{25898, abstract = {{Metal oxide inverse opals are interesting for various applications. To achieve highly ordered inverse opal structures, one important issue during the colloidal crystal templating procedure is to form a stable precursor network before the template loses its structural integrity at high temperature. Using poly(methyl methacrylate), PMMA, colloidal crystal templates, it is essential to consider the physical and chemical changes of the precursors induced by the changes of PMMA during the thermal conversion. For a systematic investigation of this matter, we synthesized a variety of metal oxide inverse opals from the respective metal nitrates, including Cr2O3, Ga2O3, Fe2O3, In2O3, CuO, CeO2, and ZnO, to compare the effect of various modifications of precursors on the structural and optical properties. When the nitrate precursors have a lower thermal stability than the PMMA template, we have modified the metal nitrates by chelating or by polyacrylamide gelation to form more stable precursor networks.}}, author = {{Zhang, Xuyang and Weinberger, Christian and Amrehn, Sabrina and Wu, Xia and Tiemann, Michael and Wagner, Thorsten}}, issn = {{1434-1948}}, journal = {{European Journal of Inorganic Chemistry}}, pages = {{3402--3407}}, title = {{{Synthesis of Metal Oxide Inverse Opals from Metal Nitrates by PMMA Colloidal Crystal Templating}}}, doi = {{10.1002/ejic.202000517}}, year = {{2020}}, } @article{25900, abstract = {{The proton conduction properties of a phosphonato-sulfonate-based coordination polymer are studied by impedance spectroscopy using a single crystal specimen. Two distinct conduction mechanisms are identified. Water-mediated conductance along the crystal surface occurs by mass transport, as evidenced by a high activation energy (0.54 eV). In addition, intrinsic conduction by proton ′hopping′ through the interior of the crystal with a low activation energy (0.31 eV) is observed. This latter conduction is anisotropic with respect to the crystal structure and seems to occur through a channel along the c axis of the orthorhombic crystal. Proton conduction is assumed to be mediated by sulfonate groups and non-coordinating water molecules that are part of the crystal structure.}}, author = {{Javed, Ali and Wagner, Thorsten and Wöhlbrandt, Stephan and Stock, Norbert and Tiemann, Michael}}, issn = {{1439-4235}}, journal = {{ChemPhysChem}}, pages = {{605--609}}, title = {{{Proton Conduction in a Single Crystal of a Phosphonato‐Sulfonate‐Based Coordination Polymer: Mechanistic Insight}}}, doi = {{10.1002/cphc.202000102}}, year = {{2020}}, } @article{25902, abstract = {{This Special Issue on “Functional Nanoporous Materials” in the MDPI journal nanomaterials features seven original papers ...}}, author = {{Weinberger, Christian and Tiemann, Michael}}, issn = {{2079-4991}}, journal = {{Nanomaterials}}, title = {{{Functional Nanoporous Materials}}}, doi = {{10.3390/nano10040699}}, year = {{2020}}, } @inproceedings{42892, abstract = {{This paper presents the results of static short-term and long-term tensile tests for beta-nucleated joined polypropylene samples by the hot plate welding process. In the present study different dimensionless joining displacements are accounted for. The results show that high short-term tensile strength does not directly transfer to high long-term tensile strength. The morphology of the weld seam in the joined samples is examined by means of transmitted and reflected light microscopy. For the dimensionless joining displacements of 0.75 and 0.95, stretched spherulites are obtained. X-Ray diffraction can be used as a tool for qualitative and quantitative analysis and eventually for differentiation of samples of various joining displacements.}}, author = {{Wübbeke, Andrea and Schöppner, Volker and Paul, André and Tiemann, Michael and Austermeier, Laura and Fitze, Marcus and Chen, Mingie and Jakob, Fabian and Heim, Hans-Peter and Wu, Tao and Niendorf, Thomas and Röhricht, Marie-Luise and Schmidt, Michael}}, booktitle = {{SPE ANTEC 2020: The Virtual Edition 5 }}, title = {{{Long- and Short-Term Tensile Strength and Morphology of Joined Beta-Nucleated Polypropylene Parts}}}, year = {{2020}}, } @article{24236, abstract = {{In diesem Artikel werden das Scherzugverhalten und der morphologische Zustand von konturgeschweißtem Polypropylen (PP) mit einem Massenanteil von 0,2% Ruß untersucht. Dabei zeigen die Ergebnisse ...}}, author = {{Schöppner, Volker and Wübbeke, Andrea and Schriegel, Fabian and Paul, Andrej and Tiemann, Michael and Geißler, Bastian and Schmidt, Michael and Magnier, Arnaud and Niendorf, Thomas }}, journal = {{Joining Plastics}}, pages = {{30--35}}, title = {{{Selected Aspects for the Assessment of Laser Transmission Welding}}}, year = {{2020}}, } @article{24100, abstract = {{Zinc oxide (ZnO) hollow spheres with defined morphology and micro-/nanostructure are prepared by a hydrothermal synthesis approach. The materials possess fine-leaved structures at their particle surface (nanowall hollow micro spheres). Morphology control is achieved by citric acid used as an additive in variable relative quantities during the synthesis. The structure formation is studied by various time-dependent ex situ methods, such as scanning electron microscopy, x-ray diffraction, and Raman spectroscopy. The fine-leaved surface structure is characterized by high-resolution transmission electron microscopy techniques (HRTEM, STEM), using a high-angle annular dark field detector, as well as by differential phase contrast analysis. In-depth structural characterization of the nanowalls by drop-by-drop ex situ FE-SEM analysis provides insight into possible structure formation mechanisms. Further investigation addresses the thermal stability of the particle morphology and the enhancement of the surface-to-volume ratio by heat treatment (examined by N2 physisorption).}}, author = {{Engelkemeier, Katja and Lindner, Jörg and Bürger, Julius and Vaupel, Kathrin and Hartmann, Marc and Tiemann, Michael and Hoyer, Kay-Peter and Schaper, Mirko}}, issn = {{0957-4484}}, journal = {{Nanotechnology}}, pages = {{095701}}, title = {{{Nano-architectural complexity of zinc oxide nanowall hollow microspheres and their structural properties}}}, doi = {{10.1088/1361-6528/ab55bc}}, volume = {{31}}, year = {{2020}}, } @article{25907, abstract = {{The combined benefits of moisture-stable phosphonic acids and mesoporous silica materials (SBA-15 and MCM-41) as large-surface-area solid supports offer new opportunities for several applications, such as catalysis or drug delivery. We present a comprehensive study of a straightforward synthesis method via direct immobilization of several phosphonic acids and phosphoric acid esters on various mesoporous silicas in a Dean–Stark apparatus with toluene as the solvent. Due to the utilization of azeotropic distillation, there was no need to dry phosphonic acids, phosphoric acid esters, solvents, or silicas prior to synthesis. In addition to modeling phosphonic acids, immobilization of the important biomolecule adenosine monophosphate (AMP) on the porous supports was also investigated. Due to the high surface area of the mesoporous silicas, a possible catalytic application based on immobilization of an organocatalyst for an asymmetric aldol reaction is discussed.}}, author = {{Weinberger, Christian and Heckel, Tatjana and Schnippering, Patrick and Schmitz, Markus and Guo, Anpeng and Keil, Waldemar and Marsmann, Heinrich C. and Schmidt, Claudia and Tiemann, Michael and Wilhelm, René}}, issn = {{2079-4991}}, journal = {{Nanomaterials}}, title = {{{Straightforward Immobilization of Phosphonic Acids and Phosphoric Acid Esters on Mesoporous Silica and Their Application in an Asymmetric Aldol Reaction}}}, doi = {{10.3390/nano9020249}}, year = {{2019}}, } @article{25904, abstract = {{We examined the effect of CaCl2 and LiCl on ice melting in mesoporous silica (MCM-41 and SBA-15 silica). For that purpose, we determined the ice melting temperature in pores of various size (pore radii between 1.9 and 11.1 nm) in water and aqueous solutions up to high total solute molality (up to about 12 mol kg–1) using differential scanning calorimetry. We found that both electrolytes reduce the ice melting temperature within the pores. An exception is the melting of ice in the smallest pores, which does not seem to be affected by the presence of solutes, most likely owing to an exclusion of the ions from entering the pores. For all other pores, we observed that the ice melting temperature decreases as a function of pore size and electrolyte concentration. Using thermodynamic considerations as well as additional experimental data we developed a parametrization that can be used to predict the ice melting point as a function of pore size and total solute molality. For that purpose, we extended a formulation of the effective water activity of aqueous solutions under mechanical pressure toward its application in confinement and tested this new parametrization on literature data.}}, author = {{Jantsch, Evelyn and Weinberger, Christian and Tiemann, Michael and Koop, Thomas}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, pages = {{24566--24574}}, title = {{{Phase Transitions of Ice in Aqueous Salt Solutions within Nanometer-Sized Pores}}}, doi = {{10.1021/acs.jpcc.9b06527}}, year = {{2019}}, } @article{25905, abstract = {{A nanocomposite material based on copper(II) oxide (CuO) and its utilization as a highly selective and stable gas-responsive electrical switch for hydrogen sulphide (H2S) detection is presented. The material can be applied as a sensitive layer for H2S monitoring, e.g., in biogas gas plants. CuO nanoparticles are embedded in a rigid, nanoporous silica (SiO2) matrix to form an electrical percolating network of low conducting CuO and, upon exposure to H2S, highly conducting copper(II) sulphide (CuS) particles. By steric hindrance due to the silica pore walls, the structure of the network is maintained even though the reversible reaction of CuO to CuS is accompanied by significant volume expansion. The conducting state of the percolating network can be controlled by a variety of parameters, such as temperature, electrode layout, and network topology of the porous silica matrix. The latter means that this new type of sensing material has a structure-encoded detection limit for H2S, which offers new application opportunities. The fabrication process of the mesoporous CuO@SiO2 composite as well as the sensor design and characteristics are described in detail. In addition, theoretical modeling of the percolation effect by Monte-Carlo simulations yields deeper insight into the underlying percolation mechanism and the observed response characteristics.}}, author = {{Paul, Andrej and Schwind, Bertram and Weinberger, Christian and Tiemann, Michael and Wagner, Thorsten}}, issn = {{1616-301X}}, journal = {{Advanced Functional Materials}}, title = {{{Gas Responsive Nanoswitch: Copper Oxide Composite for Highly Selective H2S Detection}}}, doi = {{10.1002/adfm.201904505}}, year = {{2019}}, } @article{25908, abstract = {{Herein we present a new proton-conducting iron(II) metal–organic framework (MOF) of an unusual structure formed by chains of alternating bistriazolate-p-benzoquinone anions and iron(II) cations with four axially coordinated water molecules. These chains assemble via π–π stacking between the aromatic units to form a three-dimensional grid-like network with channel pores filled with water molecules. The material was structurally characterized by single-crystal XRD analysis, and its water and thermal stability was investigated. The proton conductivity was studied by impedance measurements on needle-like single crystals. A simple but efficient measurement setup consisting of interdigital electrodes was used. The influence of the crystal orientation, temperature, and humidity was investigated. The iron(II)-MOF showed the highest proton conductivity of 3.3·10–3 S cm–1 at 22 °C and 94% relative humidity. Contrary to most known structures, the conductivity in this material is controlled by chemical properties of the pore system rather than by grain boundaries. The presented material is the starting point for further tailoring the proton-conducting properties, independent of morphological features which could find potential applications as membrane materials in proton-exchange membrane fuel cells.}}, author = {{Bunzen, Hana and Javed, Ali and Klawinski, Danielle and Lamp, Anton and Grzywa, Maciej and Kalytta-Mewes, Andreas and Tiemann, Michael and von Nidda, Hans-Albrecht Krug and Wagner, Thorsten and Volkmer, Dirk}}, issn = {{2574-0970}}, journal = {{ACS Applied Nano Materials}}, pages = {{291--298}}, title = {{{Anisotropic Water-Mediated Proton Conductivity in Large Iron(II) Metal–Organic Framework Single Crystals for Proton-Exchange Membrane Fuel Cells}}}, doi = {{10.1021/acsanm.8b01902}}, year = {{2019}}, } @article{25906, abstract = {{A composite material of copper oxide (CuO) dispersed in the nanopores of KIT-6 silica (SiO2) is used as a dosimetric sensor for the detection of hydrogen sulfide (H2S) gas in low parts per milion concentrations. The sensor principle is based on the reversible chemical conversion of CuO to CuS, which guarantees a high selectivity, and on the corresponding percolation-induced change in electronic conductance.}}, author = {{Paul, Andrej and Weinberger, Christian and Tiemann, Michael and Wagner, Thorsten}}, issn = {{2574-0970}}, journal = {{ACS Applied Nano Materials}}, pages = {{3335--3338}}, title = {{{Copper Oxide/Silica Nanocomposites for Selective and Stable H2S Gas Detection}}}, doi = {{10.1021/acsanm.9b01004}}, year = {{2019}}, } @inproceedings{25641, abstract = {{Langzeitfestigkeit von Schweißungen aus PP unter Berücksichtigung der Morphologie}}, author = {{Schöppner, Volker and Wübbeke, Andrea and Paul, Andre and Tiemann, Michael and Fitze, F. and Austermeier, Laura and Chen, M. and Jakob, F. and Heim, H.-P. and Wu, T. and Niendorf, T. and Röhricht, M-L. and Schmidt, M.}}, booktitle = {{Werkstoffwoche (2019)}}, location = {{Dresden (Deutschland)}}, title = {{{Langzeitfestigkeit von Schweißungen aus PP unter Berücksichtigung der Morphologie}}}, year = {{2019}}, } @article{41524, author = {{Engelkemeier, Katja and Lindner, Jörg K N and Bürger, Julius and Vaupel, Kathrin and Hartmann, Marc and Tiemann, Michael and Hoyer, Kay-Peter and Schaper, Mirko}}, issn = {{0957-4484}}, journal = {{Nanotechnology}}, keywords = {{Electrical and Electronic Engineering, Mechanical Engineering, Mechanics of Materials, General Materials Science, General Chemistry, Bioengineering}}, number = {{9}}, publisher = {{IOP Publishing}}, title = {{{Nano-architectural complexity of zinc oxide nanowall hollow microspheres and their structural properties}}}, doi = {{10.1088/1361-6528/ab55bc}}, volume = {{31}}, year = {{2019}}, } @article{22541, abstract = {{Monodisperse micron-sized silica particle monolayers deposited onto plasma-grown SiOx-ultra-thin films have been used as reference systems to investigate wetting, water adsorption and capillary bridge formation as a function of silica surface functionalization. 1H,1H, 2H,2H perfluorooctyltriethoxysil (FOTS) monolayers, have been deposited on the respective surfaces by means of chemical vapor deposition resulting in macroscopically low energy surfaces. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) reflection absorption spectroscopy confirmed the monolayer formation. Water adsorption isotherms were studied by a combination of in-situ FTIR reflection spectroscopy and quartz crystal microbalance (QCM) while macroscopic wetting was analysed by contact angle measurements. The comparative data evaluation indicates that the macroscopic wetting behaviour was changed as expected, however, that water nanodroplets formed both at intrinsic defects of the FOTS monolayer and at the FOTS/SiOx interface. Capillary bridges of liquid water are dominantly formed in the confined particle contact areas and between surface asperities on the particles. The comparison of wetting, adsorption and capillary bridge formation shows that the hydrophobization of porous materials by organosilane monolayers leads to the formation of morphology dependent nanoscopic defects that act as sites for preferential capillary bridge formation.}}, author = {{Giner, Ignacio and Torun, Boray and Han, Yan and Duderija, Belma and Meinderink, Dennis and Orive, Alejandro González and de los Arcos de Pedro, Maria Teresa and Weinberger, Christian and Tiemann, Michael and Schmid, Hans-Joachim and Grundmeier, Guido}}, issn = {{0169-4332}}, journal = {{Applied Surface Science}}, pages = {{873--879}}, title = {{{Water adsorption and capillary bridge formation on silica micro-particle layers modified with perfluorinated organosilane monolayers}}}, doi = {{10.1016/j.apsusc.2018.12.221}}, year = {{2019}}, } @article{25912, abstract = {{It is possible to infiltrate a guest species selectively in one pore system of bimodal mesoporous CMK-5 carbon by an optimized nanocasting procedure. The selective filling has a drastic impact on the low-angle X-ray diffraction pattern of this novel class of materials. The structures of CMK-5, CMK-5 composite materials (sulfur and SnO2 as guest species), and CMK-3 carbon were simulated to investigate the influence of the pore filling with different guest species on the diffraction pattern and compared with experimental results. Additionally, the impact of structural defects is taken into account. The nature of the guest species strongly influences the relative intensity of the diffraction peaks. It turns out that the diffraction patterns of sulfur-carbon composite materials are nearly identical as those of CMK-3 carbon, which is attributed to a similar electron density of carbon and sulfur. Thus, sulfur is an ideal guest species to investigate the selective pore filling in CMK-5 carbon.}}, author = {{Weinberger, Christian and Hartmann, Marc and Ren, Sai and Sandberg, Thomas and Smått, Jan-Henrik and Tiemann, Michael}}, issn = {{1387-1811}}, journal = {{Microporous and Mesoporous Materials}}, pages = {{24--31}}, title = {{{Selective pore filling of mesoporous CMK-5 carbon studied by XRD: Comparison between theoretical simulations and experimental results}}}, doi = {{10.1016/j.micromeso.2018.02.035}}, year = {{2018}}, }