Thomas Emmler - Academia.edu (original) (raw)
Papers by Thomas Emmler
Phys. Chem. Chem. Phys., 2015
Designing safe, compact and high capacity hydrogen storage systems is the key step towards introd... more Designing safe, compact and high capacity hydrogen storage systems is the key step towards introducing a pollutant free hydrogen technology into a broad field of applications. Due to the chemical bonds of hydrogen-metal atoms, metal hydrides provide high energy density in safe hydrogen storage media. Reactive hydride composites (RHCs) are a promising class of high capacity solid state hydrogen storage systems. Ca(BH4)2 + MgH2 with a hydrogen content of 8.4 wt% is one of the most promising members of the RHCs. However, its relatively high desorption temperature of ∼350 °C is a major drawback to meeting the requirements for practical application. In this work, by using NbF5 as an additive, the dehydrogenation temperature of this RHC was significantly decreased. To elucidate the role of NbF5 in enhancing the desorption properties of the Ca(BH4)2 + MgH2 (Ca-RHC), a comprehensive investigation was carried out via manometric measurements, mass spectrometry, Differential Scanning Calorimetry (DSC), in situ Synchrotron Radiation-Powder X-ray Diffraction (SR-PXD), X-ray Absorption Spectroscopy (XAS), Anomalous Small-Angle X-ray Scattering (ASAXS), Scanning and Transmission Electron Microscopy (SEM, TEM) and Nuclear Magnetic Resonance (NMR) techniques.
Journal of Polymer Science Part B: Polymer Physics, 2014
ABSTRACT Polymeric gas separation membranes frequently undergo the phenomenon of aging, that is, ... more ABSTRACT Polymeric gas separation membranes frequently undergo the phenomenon of aging, that is, performance parameters like permeability decrease with storage or usage time. Here, we report on a new approach of reducing aging by incorporation of functionalized multiwalled carbon nanotubes into a polymer of intrinsic microporosity. Free volume and permeability measurements clearly show a reduced aging with incorporation of the carbon nantubes. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014
European Journal of Inorganic Chemistry, 2006
The biological importance of the reactions catalysed by these enzymes led to the development of a... more The biological importance of the reactions catalysed by these enzymes led to the development of a variety ofzinc(II) complexes as functional model compounds in order to gain better understanding of the reaction mechanism. They all feature at least one zinc-thiolate linkage and one or ...
Journal of Physical Chemistry C, 2012
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 5, 2004
The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diam... more The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by 1H MAS (MAS=magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), po...
Solid State Nuclear Magnetic Resonance, 2005
The phase separation of a mixture of water and isobutyric acid (iBA) confined in the pore space o... more The phase separation of a mixture of water and isobutyric acid (iBA) confined in the pore space of Controlled Pore Glass (CPG) 10-75 has been studied by 1 H NMR relaxometry and 1 H-pulsed field gradient (PFG) diffusion measurements. For an acid-rich mixture (mass fraction 54 wt% iBA), evidence of a phase separation process in the pores was obtained, which occurs in a temperature window between 32 and 39 1C, as indicated in the PFG data by an anomalous temperature dependence of the diffusion coefficient and in the relaxation data by a bi-exponential magnetization decay. The phase separation temperature of the mixture in the pore is slightly lower than in the bulk mixture of the same composition (41 1C) and extends over a finite temperature range. A qualitative model of the phase separation process in the pores is developed, which assumes a temperature-dependent domain-like structure of the liquid below the phase transition temperature and a breakdown of these domains upon reaching the transition temperature. r 2005 Elsevier Inc. All rights reserved.
Soft Materials, 2007
Solid‐state NMR spectroscopy is employed for the structural characterization of precursor‐derived... more Solid‐state NMR spectroscopy is employed for the structural characterization of precursor‐derived Si‐B‐C‐N ceramics. Particular emphasis is given to the structural composition of the BNC x phase which plays a key role for the unusual high temperature stability of these materials. In the ...
Microchimica Acta, 2012
ABSTRACT Industrially relevant characterization of multi-walled carbon nanotubes (MWCNT) is still... more ABSTRACT Industrially relevant characterization of multi-walled carbon nanotubes (MWCNT) is still a challenging task. The aim of this work is to show novel and fast concepts for the chemical characterization of carbon nanotubes (CNT) by a combination of analytical techniques. Information obtained by individual tools like Fourier transform infrared spectroscopy (FTIR), attenuated total reflection infrared spectroscopy or Raman spectroscopy is not providing a full picture of the functionalization of MWCNTs. However, a combination of tools such as FTIR or mass spectrometry with thermogravimetric methods proved to be very useful. Sample preparation for FTIR and Raman spectroscopy is another focus of this contribution because of its strong effect on the results obtained. We also are suggesting methods for sample preparation that lead to highly reproducibility results. Measurements have been carried out on typical CNT samples such as commercially available pristine, carboxylated and amino-functionalized MWCNTs, and on polystyrenegrafted MWCNTs. The results may serve as a guidance for the qualitative and quantitative characterization of CNT. Figure 3D-TGA-FTIR image of amine functionalized MWCNT with relating TGA curve
Journal of Membrane Science, 2011
Diffusion models such as Vrentas & Duda diffusion theory and Wesselingh & Bollen multicomponent d... more Diffusion models such as Vrentas & Duda diffusion theory and Wesselingh & Bollen multicomponent diffusion model have been used together with estimated tracer diffusion coefficients in order to provide a predictive method to calculate thermodynamic diffusion coefficients needed for transport simulation in polymer membrane processes. PFG-NMR measurements were carried out in order to estimate the tracer diffusion coefficients for solvent-solvent-polymer systems on free-standing crosslinked polymer films. The use of experimentally determined diffusivities for a set of finite solvent-solvent-polymer concentrations as well as of plausible assumptions in nanofiltration allows the estimation of the unclear parameters presented in the diffusion theories with the subsequent predictability for those systems.
Chemistry - A European Journal, 2008
Mesoporous pure silicas and functionalized silica with a narrow pore size distribution centered a... more Mesoporous pure silicas and functionalized silica with a narrow pore size distribution centered at 3.8 nm were prepared by a novel template, amphiphilic dendritic polyglycerol. The resulting silica materials were characterized by electron microscopy; nitrogen adsorption; (1)H, (13)C, and (29)Si solid-state cross-polarization magic-angle spinning NMR spectroscopy. It was shown that the template could be completely removed from the pure and functionalized silica in an environmentally friendly way by means of a simple water extraction procedure. Furthermore, it was shown that these materials could be easily functionalized, for example, by employing aminopropyl groups. Thus, a new environmentally friendly pathway to this fascinating class of silica material has been opened.
Membranes, 2015
High free-volume copolymers were prepared via polycondensation with 2,3,5,6,-tetrafluoroterephtha... more High free-volume copolymers were prepared via polycondensation with 2,3,5,6,-tetrafluoroterephthalonitrile (TFTPN) in which a portion of the 3,3,3',3'-tetramethyl-1,1'-spirobisindane (TTSBI) of PIM-1 was replaced with dibutyl anthracene maleimide (4bIII). An investigation of free volume using positron annihilation lifetime spectroscopy (PALS), and gas permeation measurements was carried out for the thin film composite copolymer membranes and compared to PIM-1. The average free volume hole size and the gas permeance of the copolymer membranes increased with decreasing TTSBI content in the copolymer.
Phys. Chem. Chem. Phys., 2015
Designing safe, compact and high capacity hydrogen storage systems is the key step towards introd... more Designing safe, compact and high capacity hydrogen storage systems is the key step towards introducing a pollutant free hydrogen technology into a broad field of applications. Due to the chemical bonds of hydrogen-metal atoms, metal hydrides provide high energy density in safe hydrogen storage media. Reactive hydride composites (RHCs) are a promising class of high capacity solid state hydrogen storage systems. Ca(BH4)2 + MgH2 with a hydrogen content of 8.4 wt% is one of the most promising members of the RHCs. However, its relatively high desorption temperature of ∼350 °C is a major drawback to meeting the requirements for practical application. In this work, by using NbF5 as an additive, the dehydrogenation temperature of this RHC was significantly decreased. To elucidate the role of NbF5 in enhancing the desorption properties of the Ca(BH4)2 + MgH2 (Ca-RHC), a comprehensive investigation was carried out via manometric measurements, mass spectrometry, Differential Scanning Calorimetry (DSC), in situ Synchrotron Radiation-Powder X-ray Diffraction (SR-PXD), X-ray Absorption Spectroscopy (XAS), Anomalous Small-Angle X-ray Scattering (ASAXS), Scanning and Transmission Electron Microscopy (SEM, TEM) and Nuclear Magnetic Resonance (NMR) techniques.
Journal of Polymer Science Part B: Polymer Physics, 2014
ABSTRACT Polymeric gas separation membranes frequently undergo the phenomenon of aging, that is, ... more ABSTRACT Polymeric gas separation membranes frequently undergo the phenomenon of aging, that is, performance parameters like permeability decrease with storage or usage time. Here, we report on a new approach of reducing aging by incorporation of functionalized multiwalled carbon nanotubes into a polymer of intrinsic microporosity. Free volume and permeability measurements clearly show a reduced aging with incorporation of the carbon nantubes. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014
European Journal of Inorganic Chemistry, 2006
The biological importance of the reactions catalysed by these enzymes led to the development of a... more The biological importance of the reactions catalysed by these enzymes led to the development of a variety ofzinc(II) complexes as functional model compounds in order to gain better understanding of the reaction mechanism. They all feature at least one zinc-thiolate linkage and one or ...
Journal of Physical Chemistry C, 2012
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 5, 2004
The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diam... more The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by 1H MAS (MAS=magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), po...
Solid State Nuclear Magnetic Resonance, 2005
The phase separation of a mixture of water and isobutyric acid (iBA) confined in the pore space o... more The phase separation of a mixture of water and isobutyric acid (iBA) confined in the pore space of Controlled Pore Glass (CPG) 10-75 has been studied by 1 H NMR relaxometry and 1 H-pulsed field gradient (PFG) diffusion measurements. For an acid-rich mixture (mass fraction 54 wt% iBA), evidence of a phase separation process in the pores was obtained, which occurs in a temperature window between 32 and 39 1C, as indicated in the PFG data by an anomalous temperature dependence of the diffusion coefficient and in the relaxation data by a bi-exponential magnetization decay. The phase separation temperature of the mixture in the pore is slightly lower than in the bulk mixture of the same composition (41 1C) and extends over a finite temperature range. A qualitative model of the phase separation process in the pores is developed, which assumes a temperature-dependent domain-like structure of the liquid below the phase transition temperature and a breakdown of these domains upon reaching the transition temperature. r 2005 Elsevier Inc. All rights reserved.
Soft Materials, 2007
Solid‐state NMR spectroscopy is employed for the structural characterization of precursor‐derived... more Solid‐state NMR spectroscopy is employed for the structural characterization of precursor‐derived Si‐B‐C‐N ceramics. Particular emphasis is given to the structural composition of the BNC x phase which plays a key role for the unusual high temperature stability of these materials. In the ...
Microchimica Acta, 2012
ABSTRACT Industrially relevant characterization of multi-walled carbon nanotubes (MWCNT) is still... more ABSTRACT Industrially relevant characterization of multi-walled carbon nanotubes (MWCNT) is still a challenging task. The aim of this work is to show novel and fast concepts for the chemical characterization of carbon nanotubes (CNT) by a combination of analytical techniques. Information obtained by individual tools like Fourier transform infrared spectroscopy (FTIR), attenuated total reflection infrared spectroscopy or Raman spectroscopy is not providing a full picture of the functionalization of MWCNTs. However, a combination of tools such as FTIR or mass spectrometry with thermogravimetric methods proved to be very useful. Sample preparation for FTIR and Raman spectroscopy is another focus of this contribution because of its strong effect on the results obtained. We also are suggesting methods for sample preparation that lead to highly reproducibility results. Measurements have been carried out on typical CNT samples such as commercially available pristine, carboxylated and amino-functionalized MWCNTs, and on polystyrenegrafted MWCNTs. The results may serve as a guidance for the qualitative and quantitative characterization of CNT. Figure 3D-TGA-FTIR image of amine functionalized MWCNT with relating TGA curve
Journal of Membrane Science, 2011
Diffusion models such as Vrentas & Duda diffusion theory and Wesselingh & Bollen multicomponent d... more Diffusion models such as Vrentas & Duda diffusion theory and Wesselingh & Bollen multicomponent diffusion model have been used together with estimated tracer diffusion coefficients in order to provide a predictive method to calculate thermodynamic diffusion coefficients needed for transport simulation in polymer membrane processes. PFG-NMR measurements were carried out in order to estimate the tracer diffusion coefficients for solvent-solvent-polymer systems on free-standing crosslinked polymer films. The use of experimentally determined diffusivities for a set of finite solvent-solvent-polymer concentrations as well as of plausible assumptions in nanofiltration allows the estimation of the unclear parameters presented in the diffusion theories with the subsequent predictability for those systems.
Chemistry - A European Journal, 2008
Mesoporous pure silicas and functionalized silica with a narrow pore size distribution centered a... more Mesoporous pure silicas and functionalized silica with a narrow pore size distribution centered at 3.8 nm were prepared by a novel template, amphiphilic dendritic polyglycerol. The resulting silica materials were characterized by electron microscopy; nitrogen adsorption; (1)H, (13)C, and (29)Si solid-state cross-polarization magic-angle spinning NMR spectroscopy. It was shown that the template could be completely removed from the pure and functionalized silica in an environmentally friendly way by means of a simple water extraction procedure. Furthermore, it was shown that these materials could be easily functionalized, for example, by employing aminopropyl groups. Thus, a new environmentally friendly pathway to this fascinating class of silica material has been opened.
Membranes, 2015
High free-volume copolymers were prepared via polycondensation with 2,3,5,6,-tetrafluoroterephtha... more High free-volume copolymers were prepared via polycondensation with 2,3,5,6,-tetrafluoroterephthalonitrile (TFTPN) in which a portion of the 3,3,3',3'-tetramethyl-1,1'-spirobisindane (TTSBI) of PIM-1 was replaced with dibutyl anthracene maleimide (4bIII). An investigation of free volume using positron annihilation lifetime spectroscopy (PALS), and gas permeation measurements was carried out for the thin film composite copolymer membranes and compared to PIM-1. The average free volume hole size and the gas permeance of the copolymer membranes increased with decreasing TTSBI content in the copolymer.