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991.
用密度泛函理论优化了三苯甲烷(1)和一系列三(4-硝基苯基)甲烷衍生物2,3和4的几何结构,并计算了其红外光谱和拉曼光谱;通过与实验光谱的对比,对实验光谱中的谱峰进行了指认,并从理论上纠正了部分对3和4红外光谱谱峰不合适的实验指认;同时预测了2,3和4的拉曼光谱.结果表明,几种化合物的振动光谱计算结果与相应的实验结果吻合良好;且化合物2,3和4的拉曼光谱具有相似性. 相似文献
992.
993.
Bingqing Lin Xi Wu Prof. Dr. Lin Xie Yongqiang Kang Prof. Dr. Hongda Du Prof. Dr. Feiyu Kang Prof. Dr. Jia Li Prof. Dr. Lin Gan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20528-20532
Resolving interstitial hydrogen atoms at the surfaces and interfaces is crucial for understanding the mechanical and physicochemical properties of metal hydrides. Although palladium (Pd) hydrides hold important applications in hydrogen storage and electrocatalysis, the atomic position of interstitial hydrogen at Pd hydride near surfaces still remains undetermined. We report the first direct imaging of subsurface hydrogen atoms absorbed in Pd nanoparticles by using differentiated and integrated differential phase contrast within an aberration-corrected scanning transmission electron microscope. In contrast to the well-established octahedral interstitial sites for hydrogen in the bulk, subsurface hydrogen atoms are directly identified to occupy the tetrahedral interstices. DFT calculations show that the amount and the occupation type of subsurface hydrogen atoms play an indispensable role in fine-tuning the electronic structure and associated chemical reactivity of the Pd surface. 相似文献
994.
Dr. Long Jiao Dr. Weijie Yang Dr. Gang Wan Rui Zhang Dr. Xusheng Zheng Dr. Hua Zhou Prof. Dr. Shu-Hong Yu Prof. Dr. Hai-Long Jiang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20770-20776
Single-atom catalysts (SACs) are of great interest because of their ultrahigh activity and selectivity. However, it is difficult to construct model SACs according to a general synthetic method, and therefore, discerning differences in activity of diverse single-atom catalysts is not straightforward. Herein, a general strategy for synthesis of single-atom metals implanted in N-doped carbon (M1-N-C; M=Fe, Co, Ni and Cu) has been developed starting from multivariate metal–organic frameworks (MOFs). The M1-N-C catalysts, featuring identical chemical environments and supports, provided an ideal platform for differentiating the activity of single-atom metal species. When employed in electrocatalytic CO2 reduction, Ni1-N-C exhibited a very high CO Faradaic efficiency (FE) up to 96.8 % that far surpassed Fe1-, Co1- and Cu1-N-C. Remarkably, the best-performer, Ni1-N-C, even demonstrated excellent CO FE at low CO2 pressures, thereby representing a promising opportunity for the direct use of dilute CO2 feedstock. 相似文献
995.
Hossein Nourmohamadi Valeh Aghazadeh Mehdi D. Esrafili 《Surface and interface analysis : SIA》2020,52(3):110-118
Pyrite acts as a catalyst in the mineral processing, and the speed of ferric ion reduction and mineral decomposition increases with increasing cathodic points. In this study, the ferric ion interaction on the (100) and (110) surfaces of pyrite was studied using the density functional theory calculations. The analysis of stability, density of states, and electron density were performed to understand the interaction between the ferric ion and pyrite surfaces. The results showed that pyrite surface is chemically active and tends to absorb ferric ion between two surface sulfur atoms. The hyperconjugation between the 3d orbital of ferric ion and the 3p or 3d orbitals of surface atoms provides the conditions for the Fe3+ ion adsorption. The molecular orbital (MO) and electron density analyses indicate that the 3p orbitals of S atoms play a more important role in bonds formations relative to the 3d orbitals. The (110) surface is more active, and the adsorption energy is larger than that of surface (100), which is the result of decreased cation coordination and the presence of sulfur at the surface. Subsequently, the interaction of the Fe2+ ion, as product of Fe3+ ion reduction and its competitor for adsorption, on the surfaces was studied. The Fe2 + ion adsorbs stronger at the surface of (110), and the adsorption energies at (100) and (110) surfaces were obtained as −24 and −47 kcal/mol, respectively. In general, the Fe3+ ion is a stronger oxidizing agent than Fe2+ on pyrite surfaces. 相似文献
996.
Chong Ding Yihe Zhang Na Zhang Xinke Wang Qi Wei Youpeng Zhang 《Surface and interface analysis : SIA》2020,52(10):645-655
In this study, surface modification of coal gangue (CG) was performed with titanate coupling agent 201 (isopropyl tri(dioctylpyrophosphate) titanate), and the effects of surface modifier on mechanical properties and thermal stability of high-density polyethylene filled with CG (HDPE/CG) and high-density polyethylene filled with modified CG (HDPE/mCG) composites were investigated. The coupling agent was successfully grafted on CG surface through chemical reaction according to the analyses of Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the coupling agent can effectively enhance the hydrophobicity of surface that was verified by water contact angle beyond 90° of modified CG sample. With the introduction of coupling agent, some enhancements of tensile strength, flexural strength, and impact strength were observed in HDPE/mCG compared with HDPE/CG, due to the improved compatibility between mCG fillers and matrix. The increased storage modulus and decreased loss factor of HDPE/mCG composite further confirm the stronger interface adhesion after modification. Moreover, it is found that titanate coupling agent 201 can improve the thermal stability of HDPE/mCG composite to some extent. 相似文献
997.
Unfilled natural rubber compounds composed of conventional (CV), semi-efficient (SEV), efficient (EV) and sulfur donor (SD) vulcanization systems were heat aged to promote sulfur reversion. Rheometry, hardness, strain-strain characteristics including Mooney-Rivlin analysis, equilibrium solvent swell and Double Quantum (DQ) Nuclear Magnetic Resonance (NMR) were used to monitor crosslink density changes. A loss of crosslink density was observed by rheometry, C1, equilibrium swelling and by DQ NMR as a function of cure extent. No chain scission reactions were operating in the time/temperature conditions used. All crosslink distributions were unimodal and the network homogeneity followed the order of EV > SD > SEV > CV. The crosslink distribution narrowed during the curing process for the CV and SEV systems. Non-oxidative maturation reactions were advantageous in promoting a more random distribution of crosslinks in the polymer matrix. 相似文献
998.
A combination of knowledge on curing process of rubber mixes with novel methods of chemical analysis, a new unconventional approach to analysis of rubber vulcanization is presented in this study. Six SBR samples containing various N-tert-butyl-2-benzothiazole sulfenamide (TBBS) accelerator: sulfur ratios (within) the range of conventional (CV) sulfur vulcanization system were studied using multi-capillary column ion mobility spectrometry (MCC-IMS) technique. For these analysis, calibration/dilution curves were established. Moreover, data from MCC-IMS were correlated with other parameters of the rubber vulcanizates – their crosslink density and structure as well as their tensile strength and modulus at elongation. For such comparison, one of the reaction products from thermal decomposition of TBBS, benzothiazole was selected. Furthermore, the concentration of benzothiazole released during the vulcanization process corresponded well with the crosslink density of the rubber vulcanizates studied. It was even possible to calculate the crosslink density from the concentration of benzothiazole determined by MCC-IMS, using Boltzmann fitting curve. The presented results could be an important contribution in understanding the mechanisms occurring during rubber vulcanization, demonstrating a new approach to testing and evaluation of the process. 相似文献
999.
1000.
Giacomo Fiorin Fabrizio Marinelli José D. Faraldo-Gómez 《Journal of computational chemistry》2020,41(5):449-459
We report a methodology to calculate the free energy of a shape transformation in a lipid membrane directly from a molecular dynamics simulation. The bilayer need not be homogeneous or symmetric and can be atomically detailed or coarse grained. The method is based on a collective variable that quantifies the similarity between the membrane and a set of predefined density distributions. Enhanced sampling of this “Multi-Map” variable re-shapes the bilayer and permits the derivation of the corresponding potential of mean force. Calculated energies thus reflect the dynamic interplay of atoms and molecules, rather than postulated effects. Evaluation of deformations of different shape, amplitude, and range demonstrates that the macroscopic bending modulus assumed by the Helfrich–Canham model is increasingly unsuitable below the 100-Å scale. In this range of major biological significance, direct free-energy calculations reveal a much greater plasticity. We also quantify the stiffening effect of cholesterol on bilayers of different composition and compare with experiments. Lastly, we illustrate how this approach facilitates analysis of other solvent reorganization processes, such as hydrophobic hydration. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. 相似文献