The design of water-stable photo and electrocatalysts of metal-organic frameworks (MOFs) for its promising catalytic applications at long-term irradiations or persisted current loads is extremely ...necessary but still remains as challenging. A limited number of reports on Ti-MOF-based catalysts for water splitting are only available to explain and understand the correlation between the nature of materials and MOFs array. Herein, spherical Ti-MOFs and corresponding partially annealed hollow core-shell Ti-MOFs (Ti-MOF/D) are designed and the correlation with their photo(electro)catalytic water splitting performance is evaluated. The switchable valence state of Ti for the Ti-MOF as a function of molecular bonding is the possible reason behind the observed photocatalytic hydrogen generation and light-harvesting ability of the system. Besides, the defect state, solid core-shell mesoporous structure, and active sites of Ti-MOF help to trap the charge carriers and the reduction of the recombination process. This phenomenon is absent for hollow core-shells Ti-MOF/D spheres due to the rigid TiO
outer surface although there is a contradiction in surface area with Ti-MOF. Considering the diversity of Ti-MOF and Ti-MOF/D, further novel research can be designed using this way to manipulate their properties as per the requirements.
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The problem of collisionless absorption of ultrawideband electromagnetic pulses in the ionosphere is studied analytically. It is shown that absorption has a resonance character if the repetition rate ...of a train of pulses is equal to the frequency of the excited plasma waves.
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A study of the absorption spectrum of a weak-probe beam irradiating a two-level quantum emitter with broken inversion symmetry driven by external monochromatic high-frequency electromagnetic (e.g. ...laser) field and damped by squeezed vacuum reservoir with finite bandwidth was carried out for the case of the squeezed vacuum source being represented by a non-degenerate parametric oscillator below threshold. It was shown that this atom-driving-field system can either amplify or absorb weak probe electromagnetic radiation beam of much lower frequency than the frequency of the driving field. The shape of the absorption and amplification spectra can be controlled by the degree of the squeezed vacuum source degeneration and by the phase of the squeezing, while the switching between these two modes of operation can only be controlled by the phase of the squeezing.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We present a detailed extended X-ray absorption fine structure (EXAFS) characterization of the formation process of palladium nanoparticles (NPs) inside UiO-67 metal-organic framework (MOF). Starting ...from the initial UiO-67 structure with 10% of PdCl2bpydc moieties with grafted Pd ions replacing standard 4,4′-biphenyldicarboxylate linkers, we followed in situ H2-temperature programmed reduction (TPR) of the material. The cleavage of Pd–N and Pd–Cl bonds and simultaneous growth of the Pd–Pd contribution of metal NPs start at 200 °C. Below 300 °C metal NPs are small and are constrained inside the cavities of UiO-67, while at higher temperatures, the Pd–Pd coordination number (CN) increases to its bulk values, implying the aggregation of NPs into big palladium particles with probable destruction of MOF crystal structure. The formation of bigger particles is also confirmed by non-linear dependence of Debye-Waller parameter (DW) for Pd‒Pd contribution upon temperature.
•Pd NPs are formed inside UiO-67 pores in the temperature range from 200 to 300 °C.•Pd NPs agglomerate to bulk particles above 300 °C, destroying UiO-67 crystallinity.•Loosing of Pd‒N bonds starts earlier than that of Pd-Cl ones.•Pd NPs inside UiO-67 pores have high structural disorder.
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In this work, a series of PEGylated manganese-zinc ferrite mixed (PEG-Mn
1-x
Zn
x
Fe
2
O
4
) nanoparticles with varying concentrations of zinc ions (x = 0.0, 0.25, 0.4, 0.5, 0.75, 1.0) were ...synthesized using a solvothermal approach to investigate their physicochemical and magnetic hyperthermia properties through a range of analytical techniques, including TEM, XRF, XRD, FTIR, VSM, and magnetic hyperthermia. The PEG-Mn
1-x
Zn
x
Fe
2
O
4
nanoparticles exhibited a nearly spherical shape and diameters less than 30 nm. The particle size decreased from 27 to 11.6 nm with an increasing amount of zinc (x = 0.0–0.5). The saturation magnetization (M
S
) value decreased with the rising Zn content, ranging from 77.8 to 30.7 emu/g. The addition of zinc led to a reduction in the specific absorption rate (SAR) of the material. This decrease in the SAR parameter was associated with a decline in the intrinsic loss power (ILP) value, varying from 0.264 nH m
2
/kg for MnFe
2
O
4
to 0.037 nH m
2
/kg for ZnFe
2
O
4
. Consequently, these PEG-Mn
1-x
Zn
x
Fe
2
O
4
nanoparticles exhibit potential as candidates for magnetic fluid hyperthermia applications.
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This paper presents a new eco-friendly technique for the microfluidic synthesis of metal–organic framework MIL-88a in an aqueous medium at room temperature. Acetic acid as a modulator was used to ...control the morphology and size of the resulting particles during the synthesis. An increase of acetic acid concentration in a certain range of molar ratios leads to a decrease in the linear size of obtained particles and makes it possible to obtain a material with monodisperse porosity. The synthesized samples were comprehensively characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetry, and transmission electron microscopy. The porosity of the obtained materials was calculated according to the BET model, based on the data of low-temperature nitrogen adsorption.
The exceptional thermal and chemical stability of the UiO-66, -67 and -68 classes of isostructural MOFs
J. Am. Chem. Soc.
, 2008,
130
, 13850 makes them ideal materials for functionalization ...purposes aimed at introducing active centres for potential application in heterogeneous catalysis. We previously demonstrated that a small fraction (up to 10%) of the linkers in the UiO-67 MOF can be replaced by bipyridine-dicarboxylate (bpydc) moieties exhibiting metal-chelating ability and enabling the grafting of Pt(
ii
) and Pt(
iv
) ions in the MOF framework
Chem. Mater.
, 2015,
27
, 1042 upon interaction with PtCl
2
or PtCl
4
precursors. Herein we extend this functionalization approach in two directions. First, we show that by controlling the activation of the UiO-67-Pt we can move from a material hosting isolated Pt(
ii
) sites anchored to the MOF framework with Pt(
ii
) exhibiting two coordination vacancies (potentially interesting for C-H bond activation) to the formation of very small Pt nanoparticles hosted inside the MOF cavities (potentially interesting for hydrogenation reactions). The second direction consists of the extension of the approach to the insertion of Cu(
ii
), obtained
via
interaction with CuCl
2
, and exhibiting interesting redox properties. All materials have been characterized by
in situ
X-ray absorption spectroscopy at the Pt L
3
- and Cu K-edges.
Activation of LiCoPO4 in Air Aboraia, Abdelaziz M.; Shapovalov, V. V.; Guda, A. A. ...
Journal of electronic materials,
06/2021, Volume:
50, Issue:
6
Journal Article
Peer reviewed
LiCoPO
4
was synthesized in a short time by a microwave-assisted solvothermal technique at 220°C. The as-prepared samples are characterized as belonging to the
Pn
21
a
symmetry group, having poor ...electrochemical performance, and low specific capacity around 30 mAh/g. Further, activation at 700°C under air and argon increased the specific capacity to 57 mAh/g and 55 mAh/g, respectively. The local atomic and electronic structure of the samples before and after annealing was studied using x-ray absorption spectroscopy (XAS). The activation under air and Ar led to a phase transition from the
Pn
21
a
space group to the
Pnma
space group without changes in the Co oxidation state. Therefore, using myristic acid as a source for carbon coating, we found that there were no specific requirements for the activation atmosphere.
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39.
Development of a ReaxFF potential for Au–Pd Rusalev, Yu V; Motseyko, A V; Guda, A A ...
Journal of physics. Condensed matter,
2022-Dec-14, Volume:
35, Issue:
6
Journal Article
Peer reviewed
The bimetallic alloys often outperform their single-component counterparts due to synergistic effects. Being widely known, the Au-Pd alloy is a promising candidate for the novel heterogeneous ...nanocatalysts. Rational design of such systems requires theoretical simulations under ambient conditions.
quantum-mechanical calculations employ the density functional theory (DFT) and are limited to the systems with few tens of atoms and short timescales. The alternative solution implies development of reliable atomistic potentials. Among different approaches ReaxFF combines chemical accuracy and low computational costs. However, the development of a new potential is a problem without unique solution and thus requires accurate validation criteria. In this work we construct ReaxFF potential for the Au-Pd system based on
DFT calculations for bulk structures, slabs and nanoparticles with different stoichiometry. The validation was performed with molecular dynamics and Monte-Carlo calculations. We present several optimal parametrizations that describe experimental bulk mechanical and thermal properties, atomic order-disorder phase transition temperatures and the resulting ordered crystal structures.
The structure of Ce3+, which is responsible for the low-temperature oxygen storage capacity of ceria, was determined by high-energy-resolution fluorescence detected X-ray absorption spectroscopy at ...the Ce L3 and L1 edges. Well-defined ceria nanoparticles (rods, truncated octahedra, and cubes) were synthesized hydrothermally and promoted by platinum nanoparticles. The electronic structure of Ce3+ does not depend significantly on the nature of the exposed crystallographic planes of CeO2 particles; it does, however, differ from the electronic structure of known stable compounds containing Ce3+ ions, such as CeAlO3, Ce(NO3)3·6H2O, and Ce2Zr2O7. Theoretical simulation of Ce L1 and L3 X-ray absorption spectra, quantitative analysis of the oxygen storage capacity, and X-ray diffraction data suggest that Ce3+ ions form both at the surface and in the near-surface layer. Surface and bulk Ce3+ ions are characterized by elongated Ce–O distances in the first coordination shell and almost the same Ce–Ce distances in the second coordination shell with respect to Ce4+ in stoichiometric CeO2. Ce3+ ions on the surface of the nanoparticles surface may have a smaller number of oxygen neighbors (as low as six), while in the near-surface layer they tend to have an 8-fold coordination, thus producing oxygen deficit structures similar to Ce11O20.
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