1,459 research outputs found
Pentacene in 1,3,5-Tri(1-naphtyl)benzene: A Novel Standard for Transient EPR Spectroscopy at Room Temperature
Testing and calibrating an experimental setup with standard samples is an essential
aspect of scientifc research. Single crystals of pentacene in p-terphenyl are widely
used for this purpose in transient electron paramagnetic resonance (EPR) spectros copy. However, this sample is not without downsides: the crystals need to be grown
and the EPR transitions only appear at particular orientations of the crystal with
respect to the external magnetic feld. An alternative host for pentacene is the glass forming 1,3,5-tri(1-naphtyl)benzene (TNB). Due to the high glass transition point
of TNB, an amorphous glass containing randomly oriented pentacene molecules
is obtained at room temperature. Here we demonstrate that pentacene dissolved in
TNB gives a typical “powder-like” transient EPR spectrum of the triplet state fol lowing pulsed laser excitation. From the two-dimensional data set, it is straight forward to obtain the zero-feld splitting parameters and relative populations by
spectral simulation as well as the B1 feld in the microwave resonator. Due to the
simplicity of preparation, handling and stability, this system is ideal for adjusting the
laser beam with respect to the microwave resonator and for introducing students to
transient EPR spectroscopy
A Novel Modelling Process in Chemistry: Merging Biological and Mathematical Perspectives to Develop Modelling Competences
Models are essential in science and therefore in scientific literacy. Therefore, pupils need to
attain competency in the appropriate use of models. This so-called model–methodical competence
distinguishes between model competence (the conceptual part) and modelling competence (the
procedural part), wherefrom a definition follows a general overview of the concept of models in this
article. Based on this, modelling processes enable the promotion of the modelling competence. In this
context, two established approaches mainly applied in other disciplines (biology and mathematics)
and a survey among chemistry teachers and employees of chemistry education departments (N = 98)
form the starting point for developing a chemistry modelling process. The article concludes with
a description of the developed modelling process, which by its design, provides an opportunity to
develop students’ modelling competence
Efficient Lignin Fractionation from Scots Pine (Pinus sylvestris) Using Ammonium-Based Protic Ionic Liquid : Process Optimization and Characterization of Recovered Lignin
Lignin-based chemicals and biomaterials will be feasible alternatives to their fossil-fuelbased counterparts once their breakdown into constituents is economically viable. The existing
commercial market for lignin remains limited due to its complex heterogenous structure and lack of
extraction/depolymerization techniques. Hence, in the present study, a novel low-cost ammoniumbased protic ionic liquid (PIL), 2-hydroxyethyl ammonium lactate [N11H(2OH)][LAC], is used for the
selective fractionation and improved extraction of lignin from Scots pine (Pinus sylvestris) softwood
biomass (PWB). The optimization of three process parameters, viz., the incubation time, temperature, and biomass:PIL (BM:PIL) ratio, was performed to determine the best pretreatment conditions
for lignin extraction. Under the optimal pretreatment conditions (180 ◦C, 3 h, and 1:3 BM:PIL ratio), [N11H(2OH)][LAC] yielded 61% delignification with a lignin recovery of 56%; the cellulose
content of the recovered pulp was approximately 45%. Further, the biochemical composition of
the recovered lignin and pulp was determined and the recovered lignin was characterized using
1H–13C heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) spectroscopy, quantitative 31P NMR, gel permeation chromatography (GPC), attenuated total reflectance
(ATF)–Fourier transform infrared spectroscopy (ATR-FTIR), and thermal gravimetric analysis (TGA)
analysis. Our results reveal that [N11H(2OH)][LAC] is significantly involved in the cleavage of
predominant β–O–4’ linkages for the generation of aromatic monomers followed by the in situ
depolymerization of PWB lignin. The simultaneous extraction and depolymerization of PWB lignin
favors the utilization of recalcitrant pine biomass as feedstock for biorefinery schemes
Novel Phosphonium-Based Ionic Liquid Electrolytes for Battery Applications
In this study, we address the fundamental question of the physicochemical and electrochemical
properties of phosphonium-based ionic liquids containing the counter-ions bis(trifluoromethanesul
fonyl)imide ([TFSI]) and bis(fluorosulfonyl)imide ([FSI]). To clarify these structure–property as
well as structure–activity relationships, trimethyl-based alkyl- and ether-containing phosphonium
ILs were systematically synthesized, and their properties, namely density, flow characteristics, alkali
metal compatibility, oxidative stability, aluminum corrosivity as well as their use in Li-ion cells
were examined comprehensively. The variable moiety on the phosphonium cation exhibited a chain
length of four and five, respectively. The properties were discussed as a function of the side chain,
counter-ion and salt addition ([Li][TFSI] or [Li][FSI]). High stability coupled with good flow characteristics
were found for the phosphonium IL [P1114][TFSI] and the mixture [P1114][TFSI] + [Li][TFSI],
respectively
Novel Phosphonium-Based Ionic Liquid Electrolytes for Battery Applications
In this study, we address the fundamental question of the physicochemical and electrochemical properties of phosphonium-based ionic liquids containing the counter-ions bis(trifluoromethanesul
fonyl)imide ([TFSI]−) and bis(fluorosulfonyl)imide ([FSI]−). To clarify these structure–property as
well as structure–activity relationships, trimethyl-based alkyl- and ether-containing phosphonium
ILs were systematically synthesized, and their properties, namely density, flow characteristics, alkali
metal compatibility, oxidative stability, aluminum corrosivity as well as their use in Li-ion cells
were examined comprehensively. The variable moiety on the phosphonium cation exhibited a chain
length of four and five, respectively. The properties were discussed as a function of the side chain,
counter-ion and salt addition ([Li][TFSI] or [Li][FSI]). High stability coupled with good flow characteristics were found for the phosphonium IL [P1114][TFSI] and the mixture [P1114][TFSI] + [Li][TFSI],
respectively
Structure-Property Relation of Trimethyl Ammonium Ionic Liquids for Battery Applications
Ionic liquids are attractive and safe electrolytes for diverse electrochemical applications
such as advanced rechargeable batteries with high energy densities. Their properties that are
beneficial for energy storage and conversion include negligible vapor-pressure, intrinsic conductivity
as well as high stability. To explore the suitability of a series of ionic liquids with small ammonium
cations for potential battery applications, we investigated their thermal and transport properties.
We studied the influence of the symmetrical imide-type anions bis(trifluoromethanesulfonyl)imide
([TFSI]−) and bis(fluorosulfonyl)imide ([FSI]−), side chain length and functionalization, as well as
lithium salt content on the properties of the electrolytes. Many of the samples are liquid at ambient
temperature, but their solidification temperatures show disparate behavior. The transport properties
showed clear trends: the dynamics are accelerated for samples with the [FSI]− anion, shorter side
chains, ether functionalization and lower amounts of lithium salts. Detailed insight was obtained
from the diffusion coefficients of the different ions in the electrolytes, which revealed the formation
of aggregates of lithium cations coordinated by anions. The ionic liquid electrolytes exhibit sufficient
stability in NMC/Li half-cells at elevated temperatures with small current rates without the need
of additional liquid electrolytes, although Li-plating was observed. Electrolytes containing [TFSI]−
anions showed superior stability compared to those with [FSI]− anions in battery tests
Maser threshold characterization by resonator Q-factor tuning
Whereas the laser is nowadays an ubiquitous technology, applications for its microwave
analog, the maser, remain highly specialized, despite the excellent low-noise microwave
amplification properties. The widespread application of masers is typically limited by the need
of cryogenic temperatures. The recent realization of a continuous-wave room-temperature
maser, using NV− centers in diamond, is a first step towards establishing the maser as a
potential platform for microwave research and development, yet its design is far from optimal. Here, we design and construct an optimized setup able to characterize the operating
space of a maser using NV− centers. We focus on the interplay of two key parameters for
emission of microwave photons: the quality factor of the microwave resonator and the degree
of spin level-inversion. We characterize the performance of the maser as a function of these
two parameters, identifying the parameter space of operation and highlighting the requirements for maximal continuous microwave emission
Evidence of AlII Radical Addition to Benzene
Electrophilic AlIII species have long dominated
the aluminum reactivity towards arenes. Recently,
nucleophilic low-valent AlI aluminyl anions have showcased oxidative additions towards arenes C C and/or
C H bonds. Herein, we communicate compelling evidence of an AlII radical addition reaction to the benzene
ring. The electron reduction of a ligand stabilized
precursor with KC8 in benzene furnishes a double
addition to the benzene ring instead of a C H bond
activation, producing the corresponding cyclohexa-1,3
(orl,4)-dienes as Birch-type reduction product. X-ray
crystallographic analysis, EPR spectroscopy, and DFT
results suggest this reactivity proceeds through a stable
AlII radical intermediate, whose stability is a consequence of a rigid scaffold in combination with strong
steric protection
Установка для исследования параметров трубки Фильда
В данной работе была спроектирована и построена установка для исследования параметров трубки Фильда. Исследованы коэффициенты теплоотдачи и выведены коэффициенты эмпирического уравнения Нуссельта для частного случая.In this work, a device was designed and built for the study of the parameters of the Fild tube. The coefficients of heat transfer are studied and the coefficients of the empirical Nusselt equation for a particular case are derived
Black Titania and Niobia within Ten Minutes : Mechanochemical Reduction of Metal Oxides with Alkali Metal Hydrides
Partially or fully reduced transition metal oxides
show extraordinary electronic and catalytic properties but are
usually prepared by high temperature reduction reactions.
This study reports the systematic investigation of the fast
mechanochemical reduction of rutile-type TiO2 and H-Nb2O5
to their partially reduced black counterparts applying NaH
and LiH as reducing agents. Milling time and oxide to
reducing agent ratio show a large influence on the final
amount of reduced metal ions in the materials. For both
oxides LiH shows a higher reducing potential than NaH. An
intercalation of Li+ into the structure of the oxides was
proven by PXRD and subsequent Rietveld refinements as well
as 6
Li solid-state NMR spectroscopy. The products showed a
decreased band gap and the presence of unpaired electrons
as observed by EPR spectroscopy, proving the successful
reduction of Ti4+ and Nb5+. Furthermore, the developed
material exhibits a significantly enhanced photocatalytic
performance towards the degradation of methylene blue
compared to the pristine oxides. The presented method is a
general, time efficient and simple method to obtain reduced
transition metal oxides
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