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Electronic structure and magnetic behaviors of exfoliated MoS<sub>2</sub> nanosheets
摘要： The correlation of electronic structure and magnetic behaviors of layered molybdenum disulfide (MoS2) nanosheets, mechanically exfoliated from pristine hexagonal crystal (2H-MoS2) have been studied. Raman spectra show the energy difference (ΔE) between two Raman peaks A1g and E12g was about 20.2 cm-1, indicating the formation of mono-/bi-layered MoS2 nanosheets as obtained after mechanical exfoliation from pristine 2H-MoS2. The absence of the reflection peak (002) in X-ray diffraction patterns confirms the formation of few-layered and mono-/bi-layered MoS2 nanosheets. Mo LII-edge and S K-edge X-ray absorption near edge structure spectra of mono-/bi-layered MoS2 nanosheets show the splitting of different peaks that cause a noticeable change in their band structure. Magnetic M-H hysteresis loops measurement clearly demonstrates the increase of room temperature ferromagnetism from pristine to mono-/bi-layer MoS2, due to the existence of defects (“S”- vacancies or defects at the grain boundaries region) and the increase of DOS. UPS (He-I) measurements show the valence band maximum position increased from 1.11 eV (pristine MoS2) to 1.57 eV (mono-/bi-layered MoS2 nanosheets), whereas the surface work function (Ф) reduced from 4.85 eV (pristine MoS2) to 4.47 eV (mono-/bi-layered MoS2 nanosheets). UPS (He-II) valence band density of states (DOS) of S 3p - derived states near Fermi level (Ef). Mo 3d and S 2p XPS core level peaks shifted to higher energy with the reduction of the number of layers in exfoliated MoS2. As the number of layers decreased, valence band spectra, as well as VB-PES spectra of mono-/bi-layered MoS2 nanosheets, exhibits an enhanced DOS with reduced thickness.
关键词： UPS,VB-PES,XANES,Exfoliated MoS2-nanosheets,XPS,RT-FM
更新于2025-09-23 15:22:29
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Synthesis of 3,4-Biaryl-2,5-Dichlorothiophene through Suzuki Cross-Coupling and Theoretical Exploration of Their Potential Applications as Nonlinear Optical Materials
摘要： We report herein the efficient one-pot synthesis of 3,4-biaryl-2,5-dichlorothiophene derivatives (2a–2i) via a palladium-catalyzed Suzuki cross-coupling reaction. A series of thiophene derivatives were synthesized, starting from 3,4-dibromo-2,5-dichlorothiophene (1) and various arylboronic acids using Pd(PPh3)4 and K3PO4 with moderate to good yields. For further insights about the structure and property relationship, density functional theory (DFT) calculations were performed. A relaxed potential energy surface (PES) scan was performed to locate the minimum energy structure. A frontier molecular orbitals analysis was performed to explain the reactivity of all synthesized derivatives. As the synthesized derivatives had extended conjugations, therefore the first hyperpolarizability (βo) was calculated to investigate their potential as non-linear optical (NLO) materials and significant βo values were found for the 2b and 2g derivatives.
关键词： NLO,Pd (PPh3)4,thiophene,PES,density functional theory,Suzuki cross-coupling reaction
更新于2025-09-23 15:22:29
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Applications of Molecular Spectroscopy to Current Research in the Chemical and Biological Sciences || Geometric and Electronic Properties of Porphyrin and its Derivatives
摘要： In this chapter, we discuss protonation and substitution effects on the absorption spectra of porphyrin molecules based on density functional theory (DFT) and time-dependent DFT calculations. The results of the calculations are compared with experimental data. The calculations show that protonation of core nitrogen atoms of porphyrin and meso-substituted porphyrins produces a substantial shift in Soret and Q-absorption bands, relative to their positions in corresponding nonprotonated and nonsubstituted chromophores. A relaxed potential energy surface (RPES) scan has been utilized to calculate ground and excited state potential energy surface (PES) curves as functions of the rotation of one of the meso-substituted sulfonatophenyl groups about dihedral angles θ (corresponding to Cα─Cm─C?─C) ranging from 40 to 130°, using 10° increments. The ground state RPES curve indicates that when the molecule transitions from the lowest ground state to a local state, the calculated highest potential energy barrier at the dihedral angle of 90° is only 177 cm?1. This finding suggests that the meso-sulfonatophenyl substitution groups are able to rotate around Cm─C? bond at room temperature because the thermal energy (kBT) at 298 K is 207.2 cm?1. Furthermore, the calculations show that the geometric structure of the porphyrin is strongly dependent on protonation and the nature of the meso-substituted functional groups.
关键词： DFT calculation,protonation,PES,porphyrins,absorption
更新于2025-09-23 15:21:21
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Monolayer porphyrin assembled SPSf/PES membrane reactor for degradation of dyes under visible light irradiation coupling with continuous filtrationa?°
摘要： Porphyrin-based catalytic oxidation of hydrocarbon bonds is considered to be the most representative biomimetic catalysis. To mimic the biomimetic catalytic oxidation of nature under illumination of visible light, a monolayer of meso-tetrakis (1-methylpyridinium-4-yl) porphyrin immobilized sulfonated polysulfone/ polyethersulfone blend membrane (TMPyP@SPSf/PES) was prepared via a facile electrostatic assembly method. The visible light response region of TMPyP was expanded after it was immobilized on the SPSf/PES membrane surface, which resulted in the increase of the photocatalytic performance, and the Rhodamine B (RhB) degradation was increased from 30.0% to 93.4%. A photocatalytic membrane reactor (PMR) equipped with TMPyP@SPSf/PES membrane was employed for RhB treatment under continuous flow filtration coupling with photocatalysis, and the optimized degradation was up to 98.3%. Moreover, the TMPyP@SPSf/PES membrane can be reused for photocatalytic degradation of RhB after regeneration in TMPyP solution. More importantly, the TMPyP@SPSf/PES membrane can also efficiently degrade other cationic and anionic dyes (such as degradation of methylene blue 99.1%, acid fuchsin 96.8%). Finally, the oxidation mechanism and degradation pathway of RhB were further investigated by electron spin resonance (ESR), ultra-performance liquid chromatography and high-definition mass spectrometry (UPLC–HDMS) and gas chromatography-Mass spectrometry (GC–MS). It was revealed that the photogenerated hole (h+), superoxide radical (?O2?), and singlet oxygen (1O2) controlled the oxidation process. The degradation of RhB includes N-de-ethylate, wrecked of chromophore structures and opening-ring of benzene.
关键词： Photocatalytic membrane reactor,Biomimetic catalysis,Dye wastewater,TMPyP@SPSf/PES membrane,Electrostatic assembly
更新于2025-09-19 17:13:59
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The Synthesis of Polyethersulfone (PES) and its Derivatives as Polymer Light Emitting Diode (PLED) Material
摘要： Nowadays some types of polymer are being developed as Polymer Light Emitting Diode (PLED) materials because they have some advantages compared to small molecule organic light emitting diode (SM-OLED). Polymers which have numerous conjugated double bonds can be used as PLED materials, such as the polyethersulfone (PES) and its derivatives. Therefore, further research on the synthesis of PES and its derivatives is needed to explore their potential as PLED materials. In this research, the synthesis of polyethersulfone has been performed utilizing Microwave Assisted Organic Synthesis (MAOS) method and subsequently the synthesized PES was being transformed into the nitrated PES (PES-NO2) and the aminated PES (PES-NH2) utilizing the conventional method (reflux). The structure of the synthesized polymers was confirmed by analyzing the FT-IR and 1H-NMR spectra data. The potent of the synthesized polymers as PLED material was analyzed from fluorescence emission spectral data (in NMP, N-methyl pyrrolidone) showing the maximum emission wavelengths in the blue light of visible area, which were 444 nm (PES); 356 nm and 444 nm (PES-NO2); and 440 nm (PES-NH2). These results showed that all of the synthesized polymers have the potent to be used as PLED.
关键词： MAOS,PES-NO2,fluorescence,PES,PES-NH2,PLED
更新于2025-09-11 14:15:04
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Photoemission and Soft X-ray Absorption Spectroscopy Study of Gd-substituted Thermoelectric and Topological Bi2Te3
摘要： The electronic structures of Gd-substituted Bi2?xGdxTe3 single crystals have been investigated by employing synchrotron-radiation spectroscopies, such as soft X-ray absorption spectroscopy (XAS), soft X-ray magnetic circular dichroism (XMCD), photoemission spectroscopy (PES), and scanning photoelectron microscopy (SPEM). SPEM measurements confirm that Gd ions are substituted homogeneously in Bi2?xGdxTe3 crystals. The measured Gd 3d XAS and XMCD spectra provide evidence that the substituted Gd ions are trivalent and magnetic. The hν-dependence of the valence-band (VB) PES spectra are described well by the hν-dependent contributions of the Te 5p and Bi 6p states. A good agreement is found between the measured VB PES spectra of Bi2?xGdxTe3 and the calculated partial densities of states, revealing that the Te 5p states will play an important role in determining the thermoelectric and topological properties of Bi2?xGdxTe3.
关键词： Gd-substituted Bi2Te3,XAS,thermoelectric,topological,XMCD,PES,SPEM
更新于2025-09-10 09:29:36
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Nanolayer Research || Nanolayer Analysis by Photoelectron Spectroscopy
摘要： Photoelectron spectroscopy (PES), or photoemission spectroscopy, is one of the most important and useful techniques for investigating electronic and chemical states in solids, especially in nanolayers because of its high-energy resolution and surface sensitivity [1–5]. The physics behind PES is an application of the photoelectric effect. Through photoelectric ionization by irradiating samples with X-rays, vacuum ultraviolet (VUV) or ultraviolet (UV) light, the energies of the emitted photoelectrons are characteristic of their original electronic and chemical states. Therefore PES is one of the most sensitive and accurate techniques for measuring the energies and shapes of electronic states and molecular orbitals. X-ray photoelectron spectroscopy (XPS) was developed by Kai Siegbahn in 1957 and is used to study the energy levels of atomic core electrons, mainly in solids. Siegbahn referred to the technique as electron spectroscopy for chemical analysis (ESCA), since chemical structure can be determined by analyzing the core levels with small chemical shifts depending on the chemical environment of the atom. Siegbahn was awarded the Nobel Prize in Physics in 1981.
关键词： PES,Kai Siegbahn,ESCA,XPS,Photoelectron spectroscopy,photoelectric effect,electronic states,nanolayers,chemical states
更新于2025-09-09 09:28:46