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Efficiency and Quality Issues in the Production of Black Phosphorus by Mechanochemical Synthesis: A Multi-Technique Approach
摘要： Black phosphorus (BP) is a two-dimensional material potentially of great interest for applications in the fields of energy, sensing, and microelectronics. One of the most interesting methods to obtain BP is the conversion from red phosphorus (RP) by means of high-energy mechanochemical synthesis. To date, however, this synthesis process was not well characterized. In this work, starting from the mathematical model of energy transfer during the ball milling process, we investigate the effects on RP → BP conversion of three experimental parameters, the rotation speed, the milling time, and the weight ratio between the spheres and the milled material (BtPw ratio). The efficiency of the conversion process was verified by solid-state NMR, Raman spectroscopy, and X-ray diffraction. Whereas the first two parameters have a minor importance, the BtPw ratio plays a primary role in the RP → BP conversion. Yields approaching 100% can be obtained also with short milling times (15 min) and adequate rotation speed (e.g., 500 r.p.m.), provided that the BtPw ratio >40:1 is used. These results confirm the energy sustainability of the mechanochemical synthesis approach.
关键词： diffraction,solid-state NMR,anode,post-lithium ion batteries,Raman,mechanochemical synthesis
更新于2025-11-21 11:18:25
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Reorientational dynamics of organic cations in perovskite-like coordination polymers
摘要： Here we report the dynamics of organic cations as guest molecules in a perovskite host-framework. The molecular motion of CH3NH3+ (MAFe), (CH3)2NH2+ (DMAFe) and (CH3)3NH+ (TrMAFe) in the cage formed by KFe(CN)63? units was studied using a combination of experimental methods: (i) thermal analysis, (ii) dielectric and electric studies, (iii) optical observations, (iv) EPR and 1H NMR spectroscopy and (v) quasielastic neutron scattering (QENS). In the case of MAFe and TrMAFe, the thermal analysis reveals one solid-to-solid phase transition (PT) and two PTs for the DMAFe crystal. A markedly temperature-dependent dielectric constant indicates the tunable and switchable properties of the complexes. Also, their semiconducting properties are confirmed by a dc conductivity measurement. The broadband dielectric relaxation is analyzed for the TrMAFe sample in the frequency range of 100 Hz–1 GHz. QENS shows that we deal rather with the localized motion of the cation than a diffusive one. Three models, which concern the simultaneous rotation of the CH3 and/or NH3 group, π-flips and free rotations of the organic cation, are used to fit the elastic incoherent structure factor. The 1H NMR spin–lattice relaxation time for all compounds under study, as well as the second moments, has been measured in a wide temperature range. In all studied samples, the temperature dependence of the second moment of the proton NMR line indicated the gradual evolution of the molecular movements from the rigid state up to a highly disordered one.
关键词： quasielastic neutron scattering,phase transitions,perovskite,coordination polymers,dielectric properties,NMR spectroscopy,dynamics,organic cations
更新于2025-11-14 17:28:48
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Estimation of syringyl units in wood lignins by FT-Raman spectroscopy
摘要： Syringyl (S) lignin content and syringyl-to-guaiacyl (S/G) lignin ratio are important characteristics of wood and lignocellulosic biomass. Although numerous methods are available for estimating S lignin units and S/G ratio, in this work, a new method based on Raman spectroscopy that uses the 370 cm-1 Raman band-area intensity (370-area) was developed. The reliability of the Raman approach for determining S content was first tested by the quantitative analysis of three syringyl lignin models by sampling them, separately, in dioxane and in Avicel. Good linear correlations between the 370 cm-1 intensity and model concentrations were obtained. Next, the %S lignin units in various woods were measured by correlating the 370 cm-1 Raman intensity data with values of S units in lignin determined by three regularly used methods – thioacidolysis, DFRC, and 2D-HSQC NMR. The former two methods take into account only the monomers cleaved from β–O–4-linked lignin units whereas the NMR method reports S content on the whole cell wall lignin. When the 370-area intensities and %S values from the regularly used methods were correlated, good linear correlations were obtained (R2 = 0.767, 0.731, and 0.804, respectively, for the three methods). The correlation with the highest R2, i.e., with the 2D NMR method, is being proposed for estimating S units in wood lignins by Raman spectroscopy as, in principle, both represent of the whole cell wall lignin and not just the portion of lignin that gets cleaved to release monomers. The Raman analysis method is quick, uses minimal harmful chemicals, carried out nondestructively, and is insensitive to the wet or dry state of the sample. The only limitations are that a sample of wood contain at least 30% S and not be significantly fluorescent, although the latter can be mitigated in some cases.
关键词： NMR,Cell wall,%S,Thioacidolysis,S/G ratio,DFRC
更新于2025-11-14 15:16:37
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Nuclear Spin Singlet States in Photoactive Molecules: From Fluorescence/NMR Bimodality to a Bimolecular Spin Singlet State Switch
摘要： Nuclear spin singlet states are silent states in nuclear magnetic resonance (NMR). However, they can be probed indirectly and offer great potential for the development of contrast agents for magnetic resonance imaging (MRI). Here, we are introducing two novel concepts: Firstly, we investigate the bimodal NMR/fluorescence properties of 13C2-tetraphenylethylene. It possesses a long-lived singlet state in organic solvents, which shortens upon the addition of water. This simultaneously increases the fluorescence emission in a substantial enhancement of fluorescence. Secondly, we introduce a bimolecular singlet state switch based on 3-2H-coumarin containing an isolated proton. Upon UV-light exposure, a dimer forms leading to a coupling between two previously isolated protons. A nuclear spin singlet state can now be populated. Excitation with a wavelength of 254 nm results in partly cleavage of the molecule back into its monomer.
关键词： Photoswitches,NMR spectroscopy,Aggregation induced emission,Fluorescence,Nuclear spin singlet state
更新于2025-09-23 15:23:52
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Combination of OPSY and PhD-PHIP results in enhanced sensitivity in PHIP
摘要： Despite the large degree of polarization in PHIP experiments compared to the Boltzmann factor, the presence of a large amount of non-reacted molecules with thermal polarization is an important obstacle when dealing with very diluted samples. The feasibility of enhancing both sensitivity and resolution in a single experiment by combining two well established pulse sequences, OPSY and PHD-PHIP is presented. OPSY is used as a block for filtering the signals originated from thermally polarized protons. PhD-PHIP, on the other hand, is used as an acquisition block, increasing the resolution and further improving the sensitivity by preventing signal canceling in the presence of magnetic field inhomogeneities. Experiments in a complex sample with very low hyperpolarization levels are presented showing the excellent performance of the method.
关键词： Echo trains,PhD-PHIP,Spin dynamics,CPMG,J-spectroscopy,Hyperpolarization,Pulse sequences,Parahydrogen,SABRE,J-coupling,NMR,OPSY,PHIP
更新于2025-09-23 15:23:52
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New heteroleptic iridium(III) nitro complexes derived from fac-[Ir(NO2)3(H2O)3]
摘要： An aqueous solution of fac-[Ir(H2O)3(NO2)3] (1) was utilized as a starting material for preparation of the new heteroleptic iridium complex [Ir(H2O)(bpy)(NO2)3] (2). From alkaline solutions of 2, the salt Na[Ir(OH)(NO2)3(bpy)]·2H2O was isolated and its structure was determined by X-ray structure analysis. Structures of new compounds 2 and 3 as well as the parent complex 1 was characterized using multinuclear magnetic resonance spectroscopy and mass spectrometry. The structures of parent fac-[Ir(H2O)3(NO2)3] and complexes 2 and 3 were probed by employing density functional theory (DFT) calculations.
关键词： Nitrocomplexes,Iridium,DFT,NMR,Aquacomplexes,X-ray structure
更新于2025-09-23 15:23:52
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Li- and Mg-codoped bismuth niobate pyrochlores: Synthesis, structure, electrical properties
摘要： The structure and conductivity of the new Li- and Mg-codoped bismuth niobates Bi1.5Mg1?xLixNb1.5O7?δ (0 ≤ x ≤ 0.50) with the pyrochlore structure have been investigated. The samples were synthesized by the method of organic-inorganic precursors combustion. A structural characterization was performed using 7Li nuclear magnetic resonance (NMR) spectroscopy in combination with the ?tting of X-ray di?raction patterns. The Li+ cations dynamics were studied by temperature-dependent 7Li NMR lineshape analysis. The measurements have shown that the Li+ cations are distributed in one of two possible sublattices in the structure and are not mobile up to 120 °C. According to the results of structural analysis of the Bi1.5Mg1?xLixNb1.5O7?δ (x = 0.25; 0.50) pyrochlores the lithium atoms are distributed in the bismuth sites. The electrical properties were investigated by impedance spectroscopy method in the air, oxygen and “wet” atmospheres in the 25–750 °C temperature range. The activation energy value of dc conductivity is about 1.2–1.3 eV for the all samples and corresponds to the ionic (oxygen) conductivity at T > 400 °C. Electronic (p-type) conductivity was determined at T < 360 °C. 1H MAS NMR data and the results of the comparison of the conductivity of Li- and Mg-codoped bismuth niobates in dry and “wet” atmospheres point to the proton conductivity up to 500 °C. The dielectric permittivity ε′ values increase with lithium content from 86 (x = 0) to 143 (x = 0.5) at the same dielectric loss tanδ = 0.002 (1 MHz, 25 °C), TCC values vary from ?590 to ?530 ppm/°C in the 25–280 °C temperature range.
关键词： Conductivity,Dielectric properties,Pyrochlore,Dopant distribution,NMR spectroscopy,Bismuth niobate
更新于2025-09-23 15:23:52
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Phosphorus incorporation into graphitic material via hot pressing of graphite oxide and triphenylphosphine
摘要： It was shown, that the treatment of graphite oxide (GO) at a temperature of 1000 °C and a static pressure of 500 bar recovers the graphene layers. Addition of triphenylphosphine to GO helps in removal of oxygen during the treatment and allows introducing ca. 0.7 at% of phosphorus in the product. Most phosphorus atoms are bonded with oxygen as the 31P nuclear magnetic resonance spectrum showed. An analysis of the X-ray photoelectron P 2p spectrum additionally found the components corresponding to CeP and PeP bonding. Assembling of phosphorus atoms into nanometer clusters was con?rmed by transmission electron microscopy. Raman spectroscopy and electrical conductivity measurements revealed the n-type doping of graphitic material through the incorporation of phosphorus.
关键词： Triphenylphosphine,XPS,Phosphorus doping,NMR,Hot pressing,Graphite oxide
更新于2025-09-23 15:23:52
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The examination of molecular structure properties of 4,4′-oxydiphthalonitrile compound: combined spectral and computational analysis approaches
摘要： The synthesis process, X-ray diffraction analysis of its single crystal form and the structural properties of the 4,4'-oxydiphthalonitrile compound by Fourier transform infrared, nuclear magnetic resonance and ultraviolet-visible spectral methods were reported in this study. Density functional theory studies of the compound were carried out by designed modeling with the Becke three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional and 6-311G(d,p) basis set. Some molecular structure parameters obtained theoretically were compared with those obtained from the crystallographic analysis. Vibrational modes and wavenumbers with the aid of the potential energy distribution analysis, carbon and proton chemical shift values with diversified approaches and absorption wavelengths using Time-Dependent Density Functional and Conductor-Like Polarizable Continuum Model in different solvent media were examined theoretically. The compatibility of spectral and theoretical results was evaluated by examining the correlation coefficients. In addition, the frontier molecular orbitals energies, global reactivity parameters, molecular electrostatic potential map, the potential for non-linear optical material and some thermodynamic parameters at different temperature values of the 4,4'-oxydiphthalonitrile compound were investigated at the same theoretical level.
关键词： DFT,phthalonitrile,FT-IR,NMR,UV-Vis
更新于2025-09-23 15:22:29
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Medium viscosity effect on fluorescent properties of Sn(IV)-tetra(4-sulfonatophenyl)porphyrin complexes in buffer solutions
摘要： Supramolecular triads consisting of hydrophilic Sn(IV)-tetra(4-sulfophenyl)-porphyrin and two axial guests such as propylphenol, tyrosine, and 2-(2-hydroxyphenyl)-benzoxazole were synthesized. The structures of synthesized complexes were identified by experimental spectroscopic and quantum-chemical simulation methods, and their fluorescent properties were studied in various viscosity media (mixed phosphate buffer-glycerin solvents of different composition). The effect of axial ligand structure on the fluorescent properties of these triads (due to the hydrogen bonding or π-π stacking between the components of ?host-guest? systems) is discussed. The potential use of synthesized complexes as environmental probes of local viscosity is proposed.
关键词： synthesis,ROESY,fluorescent properties,hydrogen bonding,DOSY,2D NMR,DFT,viscosity,Sn(IV)-porphyrins
更新于2025-09-23 15:22:29