1,712 research outputs found
Zeolite-dye micro lasers
We present a new class of micro lasers based on nanoporous molecular sieve
host-guest systems. Organic dye guest molecules of
1-Ethyl-4-(4-(p-Dimethylaminophenyl)-1,3-butadienyl)-pyridinium Perchlorat were
inserted into the 0.73-nm-wide channel pores of a zeolite AlPO-5 host. The
zeolitic micro crystal compounds where hydrothermally synthesized according to
a particular host-guest chemical process. The dye molecules are found not only
to be aligned along the host channel axis, but to be oriented as well. Single
mode laser emission at 687 nm was obtained from a whispering gallery mode
oscillating in a 8-m-diameter monolithic micro resonator, in which the
field is confined by total internal reflection at the natural hexagonal
boundaries inside the zeolitic microcrystals.Comment: Accepted for publication in Phys. Rev. Let
Capillary Condensation, Freezing, and Melting in Silica Nanopores: A Sorption Isotherm and Scanning Calorimetry Study on Nitrogen in Mesoporous SBA-15
Condensation, melting and freezing of nitrogen in a powder of mesoporous
silica grains (SBA-15) has been studied by combined volumetric sorption
isotherm and scanning calorimetry measurements. Within the mean field model of
Saam and Cole for vapor condensation in cylindrical pores a liquid nitrogen
sorption isotherm is well described by a bimodal pore radius distribution. It
encompasses a narrow peak centered at 3.3 nm, typical of tubular mesopores, and
a significantly broader peak characteristic of micropores, located at 1 nm. The
material condensed in the micropores as well as the first two adsorbed
monolayers in the mesopores do not exhibit any caloric anomaly. The
solidification and melting transformation affects only the pore condensate
beyond approx. the second monolayer of the mesopores. Here, interfacial melting
leads to a single peak in the specific heat measurements. Homogeneous and
heterogeneous freezing along with a delayering transition for partial fillings
of the mesopores result in a caloric freezing anomaly similarly complex and
dependent on the thermal history as has been observed for argon in SBA-15. The
axial propagation of the crystallization in pore space is more effective in the
case of nitrogen than previously observed for argon, which we attribute to
differences in the crystalline textures of the pore solids.Comment: 10 pages, 7 figure
GROUNDWATER RESOURCES MANAGEMENT IN ARID COUNTRIES
no abstract availabl
Ammonia as a possible element in an energy infrastructure: catalysts for ammonia decomposition
The possible role of ammonia in a future energy infrastructure is discussed. The review is focused on the catalytic decomposition of ammonia as a key step. Other aspects, such as the catalytic removal of ammonia from gasification product gas or direct ammonia fuel cells, are highlighted as well. The more general question of the integration of ammonia in an infrastructure is also covered
Fingerprinting the magnetic behavior of antiferromagnetic nanostructures using remanent magnetization curves
Antiferromagnetic (AF) nanostructures from Co3O4, CoO and Cr2O3 were prepared
by the nanocasting method and were characterized magnetometrically. The field
and temperature dependent magnetization data suggests that the nanostructures
consist of a core-shell structure. The core behaves as a regular
antiferromagnet and the shell as a two-dimensional diluted antiferromagnet in a
field (2d DAFF) as previously shown on Co3O4 nanowires [Benitez et al., Phys.
Rev. Lett. 101, 097206 (2008)]. Here we present a more general picture on three
different material systems, i.e. Co3O4, CoO and Cr2O3. In particular we
consider the thermoremanent (TRM) and the isothermoremanent (IRM) magnetization
curves as "fingerprints" in order to identify the irreversible magnetization
contribution originating from the shells. The TRM/IRM fingerprints are compared
to those of superparamagnetic systems, superspin glasses and 3d DAFFs. We
demonstrate that TRM/IRM vs. H plots are generally useful fingerprints to
identify irreversible magnetization contributions encountered in particular in
nanomagnets.Comment: submitted to PR
Advancing Critical Chemical Processes for a Sustainable Future: Challenges for Industry and the Max Planck–Cardiff Centre on the Fundamentals of Heterogeneous Catalysis (FUNCAT)
Catalysis is involved in around 85 % of manufacturing industry and contributes an estimated 25 % to the global domestic product, with the majority of the processes relying on heterogeneous catalysis. Despite the importance in different global segments, the fundamental understanding of heterogeneously catalysed processes lags substantially behind that achieved in other fields. The newly established Max Planck–Cardiff Centre on the Fundamentals of Heterogeneous Catalysis (FUNCAT) targets innovative concepts that could contribute to the scientific developments needed in the research field to achieve net zero greenhouse gas emissions in the chemical industries. This Viewpoint Article presents some of our research activities and visions on the current and future challenges of heterogeneous catalysis regarding green industry and the circular economy by focusing explicitly on critical processes. Namely, hydrogen production, ammonia synthesis, and carbon dioxide reduction, along with new aspects of acetylene chemistry
Electronic structure and optical properties of lightweight metal hydrides
We study the electronic structures and dielectric functions of the simple
hydrides LiH, NaH, MgH2 and AlH3, and the complex hydrides Li3AlH6, Na3AlH6,
LiAlH4, NaAlH4 and Mg(AlH4)2, using first principles density functional theory
and GW calculations. All these compounds are large gap insulators with GW
single particle band gaps varying from 3.5 eV in AlH3 to 6.5 eV in the MAlH4
compounds. The valence bands are dominated by the hydrogen atoms, whereas the
conduction bands have mixed contributions from the hydrogens and the metal
cations. The electronic structure of the aluminium compounds is determined
mainly by aluminium hydride complexes and their mutual interactions. Despite
considerable differences between the band structures and the band gaps of the
various compounds, their optical responses are qualitatively similar. In most
of the spectra the optical absorption rises sharply above 6 eV and has a strong
peak around 8 eV. The quantitative differences in the optical spectra are
interpreted in terms of the structure and the electronic structure of the
compounds.Comment: 13 pages, 10 figure
A low‐cost environmental chamber to simulate warm climatic conditions
Environmental chambers are used for a variety of experiments in multiple disciplines but are often prohibitively expensive. In this study, we developed an environmental chamber that allows reliable regulation of temperature and relative humidity in a range typical for warm climatic conditions. As we have only used consumer products, which are readily available off the shelf, the device is affordable (<€900) and easy to replicate. The presented chamber has inner dimensions of 1,790 × 970 × 520 mm (height × width × depth). It is heated with two infrared lamps, and for moistening, an ultrasonic mister is used. Air dehumidification and cooling down to ambient temperature are realized with inflowing compressed laboratory air. Additionally, we installed a Peltier element cooling system to enable temperatures below the ambient laboratory temperature. The chamber works in a temperature and humidity range of 15–50 °C and 10–95%, respectively
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