显示样式:     当前期刊: "物化"类期刊    排序: 导出
我的关注
我的收藏
您暂时未登录!
登录
  • Dissolution Dynamic Nuclear Polarization at Room Temperature Using Photoexcited Triplet Electrons
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    Makoto Negoro, Akinori Kagawa, Kenichiro Tateishi, Yoshiki Tanaka, Tomohiro Yuasa, Keigo Takahashi, Masahiro Kitagawa
    更新日期:2018-04-20
  • Hybrid Density Functional Study of the Local Structures and Energy Levels of CaAl2O4:Ce3+
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    Bibo Lou, Weiguo Jing, Liren Lou, Yongfan Zhang, Min Yin, Chang-Kui Duan
    更新日期:2018-04-20
  • Electronic Spectra of Cs2NaYb(NO2)6: Is There Quantum Cutting?
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    Yuxia Luo, Zhenyu Liu, Sam Chun-Kit Hau, Yau Yuen Yeung, Ka-Leung Wong, Kwok Keung Shiu, Xueyuan Chen, Haomiao Zhu, Guochen Bao, Peter A. Tanner
    更新日期:2018-04-20
  • Natural Bond Orbital Theory of Pseudo Jahn-Teller Effects
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    Frank Weinhold, Davood Nori-Shargh

    We describe a unified picture of symmetry-breaking electronic interactions that are usually described as “pseudo Jahn-Teller (PJT) effects” and attributed to vibronic coupling, but can also be associated with hyperconjugative donor-acceptor interactions in the framework of natural bond orbital (NBO) and natural resonance theory (NRT) analysis. We show how NBO/NRT descriptors offer a simplified alternative to the vibronic coupling picture of PJT effects that yields both improved cause-effect specificity and chemically enriched understanding of symmetry-breaking phenomena, but with no necessary input from ground-state vibrational or excited-state electronic properties. Comparative NBO/NRT vs. vibronic coupling analyses of PJT effects are illustrated for two well-known cases: trans-bending in Si2H4 and higher Group-14 homologs of ethylene, and chain-kinking in cyclopentadienylideneketene (C5H4CCO) and related cumulene ketones. The conceptual and practical advantages of the NBO-based hyperconjugative approach may be expected to extend to numerous PJT-type symmetry-breaking phenomena throughout the chemical sciences.

    更新日期:2018-04-20
  • Ground-State Charge-Density Distribution in a Crystal of the Luminescent Ortho-Phenylenediboronic Acid Complex with 8-Hydroxyquinoline
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    Katarzyna N. Jarzembska, Radosław Kamiński, Krzysztof Durka, Krzysztof Wozniak

    This contribution is devoted to the first electron density studies of a luminescent oxyquinolinato boron complex in the solid state. Ortho-phenylenediboronic acid mixed with 8-hydroxyquinoline in dioxane forms high quality single crystals via slow solvent evaporation, which allows successful high resolution data collection (sin⁡θ/λ = 1.2 Å−1) and charge density distribution modelling. Particular attention has been paid to the boron-oxygen fragment connecting the two parts of the complex, and to the solvent species exhibiting anharmonic thermal motion. The experiment and theory compared rather well in terms of atomic charges and volumes, except for the boron centres. Boron atoms, as expected, constitute the most electron-deficient species in the complex molecule, whereas the neighbouring oxygen and carbon atoms are the most significantly negatively charged ones. This part of the molecule appears to be very much involved in the charge transfer occurring between the acid fragment and oxyquinoline moiety leading to the observed fluorescence, as supported by the TDDFT results and the generated transition density maps. TDDFT calculations indicated that p-type atomic orbitals contributing to the HOMO-1, HOMO and LUMO play the major role in the lowest energy transitions, and enabled further comparison with the charge density features, which is discussed in details. Furthermore, the results confirmed the known fact the Q ligand character is most important for the spectroscopic properties of this class of complexes.

    更新日期:2018-04-20
  • The Strength of Hydrogen Bonds Between Fluoro-Organics and Alcohols, a Theoretical Study
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    Robert Evan Rosenberg

    Fluorinated organic compounds are ubiquitous in the pharmaceutical and agricultural industries. To better discern the mode of action of these compounds it is critical to understand the strengths of hydrogen bonds involving fluorine. There are only a few published examples of the strengths of these bonds. This study provides a high level ab initio study of inter- and intramolecular hydrogen bonds between RF and R’OH, where R and R’ are aryl, vinyl, alkyl, and cycloalkyl. Intermolecular binding energies average near 5 kcal/mol, while intramolecular binding energies average about 3 kcal/mol. Inclusion of zero-point energies and applying a counterpoise correction lessen the difference. In both series, modest increases in binding energies are seen with increased acidity of R’OH and increased electron donation of R in RF. In the intramolecular compounds, binding energy increases with the rigidity of the F-(C)n-OH ring. Inclusion of free energy corrections at 298 K result in exoergic binding energies for the intramolecular compounds and endoergic binding energies for the intermolecular compounds. Parameters such as bond lengths, vibrational frequencies, and atomic populations are consistent with formation of a hydrogen bond, and with slightly stronger binding in the intermolecular cases over the intramolecular cases. However, these parameters correlated poorly with binding energies.

    更新日期:2018-04-20
  • A Comprehensive Scope of Peripheral and Axial Substituent Effect on the Spectroelectrochemistry of Boron Subphthalocyanines
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    Kathleen L. Sampson, Xiaoqin Jiang, Esmeralda Bukuroshi, Aleksa Dovijarski, Hasan Raboui, Timothy P Bender, Karl M. Kadish

    An extensive study of the electrochemical and spectroelectrochemical properties of 14 boron subphthalocyanine (BsubPc) derivatives with various axial and peripheral substituents was performed in 1,2-dichloromethane (CH2Cl2) containing 0.1 M tetra-n-butyl-ammonium perchlorate (TBAP) as the supporting electrolyte. From the cyclic voltammetry results, all compounds exhibit one oxidation and at least two reduction processes within the solvent potential window of +1.6 to -1.8 V vs. SCE. It was found that the reversibility of the redox reactions depends on the axial and peripheral substituents and the dipole moment of the boron-to-axial substituent. In general, UV-visible absorption spectra of the singly reduced BsubPc derivatives exhibit three equal-intensity peaks in the 450 to 650 nm region that are derived from the maximum BsubPc absorbance peak upon reduction. Axial substituents affect the intensity of the three peaks upon reduction, while peripheral substituents shift the position of the peaks to higher wavelengths. Upon oxidation, the UV-visible absorption profile flattens considerably with only a single broad (~300 nm) band apparent. Understanding the effect of substituents on the stability of the redox processes of BsubPcs will aid in further development of these materials for applications in organic electronic devices.

    更新日期:2018-04-20
  • Ultrafast Dynamics of the MLCT Excited States of Ir(III) Proteo and Deutero Dihydrides
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    Chelsea Marie Taliaferro, Evgeny O. Danilov, Felix N. Castellano

    For decades, transition metal hydrides have been at the forefront of numerous photocatalytic reactions leveraging either photoacid or photohydride generation. Of upmost importance is the nature of the M-H bond itself, which is typically the major site of photochemical reactivity, particularly in Ir(III) hydrides featuring metal-to-ligand charge transfer (MLCT) excited states. As a departure point for understanding the fundamental spectroscopy and photophysics of the MLCT excited states of Ir(III) diimine hydrides, cis-[Ir(bpy)2H2]+ (bpy = 2,2’-bipyridine) and its deuterated analog cis-[Ir(bpy)2D2]+ were prepared and investigated. The robust nature of these molecules enabled detailed solution-based photophysical studies using ultrafast transient absorption and infrared spectroscopy, executed without the generation of permanent photoproducts. Static FT-IR and Raman spectra (λex = 785 nm) of these two molecules revealed weak but measurable Ir-H and Ir-D stretching vibrations centered at 2120 cm-1 and 1510 cm-1, respectively. Short-lived (τ = 25 ps) MLCT excited states were observed for both cis-[Ir(bpy)2H2]+ and cis-[Ir(bpy)2D2]+ following femtosecond pulsed laser excitation at 480 nm in visible and near-IR transient absorption experiments. A similar time constant was measured for the in-phase and out-of-phase Ir-H stretching modes of the triplet excited state between 1900 and 2200 cm-1 using transient IR spectroscopy. The Ir-D stretching modes in the MLCT excited state were masked by bpy-localized vibrations rendering quantitative evaluation of these modes difficult. The time-resolved infrared data were consistent with DFT-calculated mid-IR difference spectra in both of these molecules, yielding quantitative matches to the measured IR difference spectra. The information presented here provides valuable insight for understanding the primary photophysical events and transient absorption and IR spectroscopic signatures likely to be encountered throughout metal hydride photochemistry.

    更新日期:2018-04-20
  • Probing Triplet Excited States and Managing Blue Light Emission of Neutral Tetradentate Platinum(II) Complexes
    J. Phys. Chem. Lett. (IF 9.353) Pub Date : 2018-04-19
    Cong You, Fang Xia, Yue Zhao, Yin Zhang, Yongjian Sheng, Yipei Wu, Xiao-Chun Hang, Fei Chen, Huili Ma, Kang Shen, Zhengyi Sun, Takahiro Ueba, Satoshi Kera, Cong Zhang, Honghai Zhang, Zhi-Kuan Chen, Wei Huang
    更新日期:2018-04-20
  • Prospects for Mitigating Intrinsic Organic Decomposition in Methylammonium Lead Triiodide Perovskite
    J. Phys. Chem. Lett. (IF 9.353) Pub Date : 2018-04-19
    John A McLeod, Lijia Liu

    Organometallic lead halide perovskites seem to be on the threshold of becoming viable commercial photovoltaics, however further improvements to the stability of these materials must be made before they can compete with existing photovoltaic technologies. Of the organometallic lead halide perovskites used in photovoltaics, methylammonium lead triiodide perovskite (MAPI) is perhaps the most studied, and understanding how MAPI degrades is crucial for developing strategies to improve stability. We discuss the experimental evidence behind several possible routes for MAPI to degrade into \ce{PbI2} and various organics, and how the decomposition path of MAPI may strongly depend on substrate, precursors, intrinsic organic defects, and morphology. Exploring the conditions required for MAPI to degrade according to a particular pathway is important not only from a fundamental materials chemistry perspective, but also for understanding intrinsic instability in MAPI-based photovoltaics and to develop strategies to improve stability.

    更新日期:2018-04-20
  • Correlated Molecular Structural Motions for Photoprotection After Deep-UV Irradiation
    J. Phys. Chem. Lett. (IF 9.353) Pub Date : 2018-04-19
    Longteng Tang, Yanli Wang, Liangdong Zhu, Che Lee, Chong Fang

    Exposure to ultraviolet (UV) light could cause photodamage to biomolecular systems and degrade optoelectronic devices. To mitigate such detrimental effects from the bottom up, we strategically select a photosensitive molecule pyranine and implement femtosecond electronic and Raman spectroscopies to elucidate its ultrafast photoprotection mechanisms in solution. Our results show that pyranine undergoes excited state proton transfer (ESPT) in water while this process is blocked in methanol regardless of excitation wavelengths (267, 400 nm). After 267 nm irradiation, the molecule relaxes from a higher lying electronic state into a lower lying singlet state with a <300 fs time constant followed by solvation events. Transient Raman marker bands exhibit different patterns of intensity dynamics and frequency shift which elucidate the real-time interplay among conformational motions, photochemical reaction and vibrational cooling after excitation. More energetic photons are revealed to selectively enhance certain relaxation pathways. These mechanistic findings offer new guidelines to improve the UV tolerance and stability of the engineered functional molecules in materials and life sciences.

    更新日期:2018-04-20
  • 更新日期:2018-04-20
  • Approach to Estimation of Hamaker Constant as Taking Hofmeister Effects into Account
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Yaxue Luo, Xiaodan Gao, Rui Tian, Hang Li
    更新日期:2018-04-20
  • Electron-Enhanced Atomic Layer Deposition of Boron Nitride Thin Films at Room Temperature and 100 °C
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Jaclyn K. Sprenger, Huaxing Sun, Andrew S. Cavanagh, Alexana Roshko, Paul T. Blanchard, Steven M. George
    更新日期:2018-04-20
  • Probing Charge Delocalization in Solid State Polychromophoric Cation Radicals Using X-ray Crystallography and DFT Calculations
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Lena V. Ivanova, Denan Wang, Sergey Lindeman, Maxim V. Ivanov, Rajendra Rathore
    更新日期:2018-04-20
  • Active Site Ensembles Enabled C–C Coupling of CO2 and CH4 for Acetone Production
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Yuntao Zhao, Hua Wang, Jinyu Han, Xinli Zhu, Qingfeng Ge
    更新日期:2018-04-20
  • 更新日期:2018-04-20
  • Comment on “The Complexity of the CaF2:Yb System: A Huge, Reversible, X-ray Induced Valence Reduction”
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Pavel P. Fedorov, Alexandr I. Ryskin

    Recently, MacKeen et al. published the paper. This comment indicates the deficit of References and contains some doubts about the proposed model.

    更新日期:2018-04-20
  • Evaluating Water Reactivity at Silica Surfaces Using Reactive Potentials
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Thiruvilla S Mahadevan, Jincheng Du

    Understanding the interactions between amorphous silica surfaces and water provides insight into material degradation of glassy materials in aqueous environment such as corrosion of nuclear waste glasses. Molecular dynamics (MD) simulations of water and nanometer sized silica structures were used in this work to evaluate the reactivity of silica flat and surfaces with curvature. We compared two dissociable water/silica potentials, namely the Reactive Force Field (ReaxFF) and the Mahadevan-Garofalini water/silica force field (MGFF) that have been in development over the last decade, to study their performance in simulating bulk water as well as silica-water interactions. Significant differences in the properties of bulk water that had a bearing on the surface interactions were observed between the two types of potentials, as well in the same potential type with two parameterization for ReaxFF, suggesting need of improvement of the existing water/silica ReaxFF potentials. Our simulation results show that a majority of the silanols were formed by reaction between water and a strained siloxane bonds that mainly exist on the surface of amorphous silica, within a few nanoseconds of the simulation time scale, in agreement with previous studies. Effect of surface curvature on the reactivity with water was investigated. Our results indicate that defect concentration at the surface bears a strong correlation to the concentration of silanols (Si-OH) that eventually form. We observe undercoordinated Si at the surface that are attacked by water before the hydrolysis reaction of the siloxane bonds and demonstrate possible mechanisms of water reacting with these undercoordinated Si. We also find that the method of generating surfaces in simulation determines the defect concentration and hence influences the reactivity of the amorphous silica surface.

    更新日期:2018-04-20
  • Computational and Experimental Investigations of the Role of Water and Alcohols in the Desorption of Heterocyclic Aromatic Compounds from Kaolinite in Toluene
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Mateus R. Lage, Gustave Kenne Dedzo, Stanislav R. Stoyanov, WenJuan Huang, Sergey Gusarov, José Walkimar de M. Carneiro, Christian Detellier, Andriy Kovalenko

    Non-aqueous extraction is an attractive alternative to the currently employed warm water process for extraction of bitumen from oil sands, as it could use less energy and water. Hydroxylated cosolvents, such as alcohols, that compete for the adsorptive clay surfaces and help release bitumen components could help improve bitumen recovery. The water naturally present in oil sand also affects oil-mineral interactions. Electronic structure methods and the statistical-mechanical 3D-RISM-KH molecular theory of solvation as well as experimental desorption measurements are employed to study the effects of water and aliphatic alcohol cosolvents in toluene solvent on the desorption of fused pyridinic heterocycles (ArN) from kaolinite. The geometries of phenanthridine and acridine (representative of pyridinic heterocycles of petroleum asphaltenes) adsorbed on the kaolinite clay surface are optimized in periodic boundary conditions using density functional theory. The 3D-RISM-KH method is employed to calculate the solvation free energy and potential of mean force for adsorption of the heterocycles on kaolinite in pure and alcohol-containing toluene. The potentials of mean force show that the adsorption of the fused pyridines on kaolinite is stronger in pure toluene than in toluene mixed with aliphatic alcohol. Analysis of the mechanism of desorption of phenanthridine and acridine from kaolinite in toluene containing alcohol reveals that the alcohol stabilizes both the pyridinic moiety and kaolinite platelet by hydrogen bonding, thus disrupting the ArN…HO-Al(kaolinite) hydrogen bond. A mechanism for retention of toluene on kaolinite is also highlighted. Experimental studies of the desorption of fused pyridines from an ArN-kaolinite aggregate show that in water-saturated toluene the rate of desorption of the phenanthridine from kaolinite is twice as high as that in dry toluene. The experimental and computational results show that water and aliphatic alcohols in toluene help desorb pyridinic heterocycles from kaolinite, a clay mineral abundant in the oil sands. The presented insights are valuable for understanding the molecule-clay interactions in solution and relevant to improving the non-aqueous extraction of bitumen from oil sand.

    更新日期:2018-04-20
  • Study of the Nature of High-Silica H-Y Acid Sites in Dimethoxymethane Carbonylation by NH3 Poisoning
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Zhiqiang Xie, Congbiao Chen, Bo Hou, Dekui Sun, Heqin Guo, Jungang Wang, Debao Li, Litao Jia

    The nature of high-silica H-Y acid sites in dimethoxymethane carbonylation is investigated by NH3 poisoning with a combination of reaction results, diffuse reflection infrared Fourier transform spectra and NH3 temperature programmed desorption. After NH3 poisoning of H-Y, ammonia desorption of zeolites NH4-Y was conducted at different temperatures in order to obtain catalysts HNH4-Y that gradually exposed different acid sites. The zeolites thus produced catalyzed dimethoxymethane carbonylation with a linear dependence of the conversion on the ammonia desorption temperature before the plateau stage. It was observed that strong Brønsted acids in zeolite Y catalyzed the reaction more selectively toward the main product methyl methoxyacetate and weak Brønsted acids catalyzed the reaction more selectively toward the byproduct methyl formate. Furthermore, the turnover frequency of Brønsted acids varied significantly among the Brønsted acids and decreased with acid strength. This finding suggested that only 10.1%-18.3% of the total Al in zeolite Y with Si/Al ratios of 15, 30 and 40 contributed to the total framework of Brønsted acids.

    更新日期:2018-04-20
  • The Interaction of CO2 with CeO2 Powder Explored by Correlating Adsorption and Thermal Desorption Analyses
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Danielle Schweke, Shimon Zalkind, Smadar Attia

    Understanding the interplay between thermodynamics and kinetics is of high importance for the optimization of catalytic reactions involving adsorption of CO2 on CeO2 (ceria). The present study explores the interaction of CO2 with ceria powder in near-realistic conditions by correlating adsorption and thermal desorption analyses. Activation energies for desorption Ea and kinetic parameters (adsorption time constants and sticking coefficients) are determined using a new methodology, based on surface science models. The sticking coefficients obtained for CO2 on ceria powder are significantly lower than for CO2 on flat surfaces. CO2 is found to adsorb most rapidly on sites attributed to surface defects. CO2 adsorption is slower on non-defective active sites, leading to the formation of various carbonate species. The desorption analysis indicates that each peak in the CO2-TPD profiles is composed of several sub-peaks, resulting from various binding sites for CO2 on the polycrystalline powder. The distribution of the chemisorbed CO2 species between the different sites, the corresponding adsorption energies and the influence of coverage on those energies are thus determined. In addition, the correlation between adsorption and desorption analyses indicates the influence of heating on the distribution of the chemisorbed species.

    更新日期:2018-04-20
  • Pourbaix Diagrams for H2O Oxidation to Adsorbed OH on Pt(111) and Why They Differ from Those for Bulk Solids.
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Alfred B Anderson

    Density functional calculations show that Pourbaix diagrams for reactions involving surface species are not the same as for bulk solids. This finding is based on calculations the onset potentials over the pH range 0 to 14 for fifteen water oxidation reactions forming OH(ads) + H+(aq) + e- on Pt(111). The deviations are results of the dependencies of Gibbs energies of adsorbed reactants on the electrode potential, causing their activities to change with potential instead of being fixed at unity, which is the case for Pourbaix diagrams of solids. In a sense, the redox couple changes as the electrode potential changes because at each potential the adsorbed reactants and products have new structures.

    更新日期:2018-04-20
  • Cation Conformational Changes of 1-Butyl-3-methylimidazolium Halides at High Pressures
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Fengjiao Chen, Guoyong Fang, Zhipeng Yan, Yuexiao Pan, Jian-Bo Liu, Lin Wang

    The cation structure changes of two 1-butyl-3-methylimidazolium halides: [BMIM]Cl and [BMIM]Br, are investigated by the in situ Raman spectroscopy, infrared spectroscopy, and synchrotron X-ray diffraction as a function of hydrostatic pressure, respectively. The [BMIM]+ cations of [BMIM]Cl take the TT conformer under ambient conditions, undergo significant changes at 3.4 GPa, which is related to the potential formations of some new cation conformations, and possess another conformation from 6.8 to 35.6 GPa. Correspondingly, crystalline [BMIM]Cl has a structure transition at 3.4 GPa, originating directly from the cation conformational changes. The [BMIM]+ cations totally transform into the GT conformer, if the diamond anvil cell-loaded sample is treated at 423 K for 12 hours in a furnace before being cooled down to room temperature. It is the first time to observe the complete conformational transition from one conformer (TT) to another (GT) for the [BMIM]+ salts in experiments. The cations preserve the GT conformation as pressure reaches 44.6 GPa for heat-treated [BMIM]Cl. As a comparison, with and without the heat treatment, the [BMIM]+ cations of [BMIM]Br keep the GT conformation at high pressures up to 29.6 GPa, as it is a relatively stable state. Moreover, a notable photoluminescence emerges at high pressures over 20.0 GPa and maintain in the decompression process, as a result of the pressure-induced polymerization of a small portion of the [BMIM]+ cations.

    更新日期:2018-04-20
  • Ammonium Perchlorate as an Effective Addition for Enhancing the Combustion and Propulsion Performance of Al/CuO Nanothermites
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Ji Dai, Fei Wang, Chengbo Ru, Jianbing Xu, Chengai Wang, Wei Zhang, Yinghua Ye, Ruiqi Shen

    Nanothermites are attracting much attention because of the high energy density, self-sustained exothermic reaction and high combustion temperature. However, they suffer from sintering and incomplete combustion, leading to poor reactivity and low energy utilization efficiency. In order to enhance the energy output and combustion performance of nanothermites, ammonium perchlorate (AP) was introduced into the Al/CuO nanothermits. The nanothermites with varied content of AP were prepared by electrospray. The morphological characterization of the nanothermites confirms that the nanoparticles are homogenously mixed without agglomeration. Heat release, specific impulse, and peak pressure of gaseous products exhibit remarkable enhancement with increasing AP content. Specifically, the nanothermites with 7.5 wt% AP produces specific impulse and heat energy of ~2.7 and ~1.4 times higher than those of Al/CuO-based nanothermites without AP. In addition, the ignition delay time of the nanothermites containing AP is not greatly increased, enabling fast response during practical applications. Thermal analysis implies that the thermite reaction between Al and CuO can be divided into two steps in the presence of AP: solid-solid phase and liquid-solid phase diffusion reaction. These results provide facile strategy to enhance the output performance of nanothermites, which may facilitate the practical propulsion and combustion applications of nanothermites.

    更新日期:2018-04-20
  • Chemical Instability of an Interface Between Silver and Bi2Se3 Topological Insulator at Room Temperature
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Katja Ferfolja, Matjaz Valant, Iuliia Mikulska, Sandra Gardonio, Mattia Fanetti

    Understanding an interaction at an interface between a topological insulator and a metal is of critical importance when designing electronic and spintronic devices or when such systems are used in catalysis. In this paper, we report on a chemical instability of the interface between Bi2Se3 and Ag studied by X-Ray Powder Diffraction and Electron Microscopy. We present strong experimental evidence of a redox solid-state reaction occurring at the interface with kinetics that is significant already at room temperature. The reaction yields Ag2Se, AgBiSe2 and Bi. The unexpected room-temperature chemical instability of the interface should be considered for all future theoretical and applicative studies involving the interface between Bi2Se3 and Ag.

    更新日期:2018-04-20
  • Temperature Effect on Transport, Charging and Binding of Low-Energy Electrons Interacting with Amorphous Solid Water Films
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Roey Sagi, Michelle Akerman Sykes, Sujith Ramakrishnan, Micha Asscher

    The charging of solid molecular films grown on grains is an important phenomenon observed in astrochemical processes that take place in interstellar space and is relevant in high altitude environmental physics and chemistry. In this work, we present temperature dependence study of both the conductivity and capacitance of Amorphous Solid Water (ASW) films (hundreds of monolayers thick) deposited on a Ru(0001) substrate. These layers subsequently interact with low-energy electrons (5 eV) at the temperature range 50-120 K under Ultra-High Vacuum (UHV) conditions. The charging of the ASW films was measured via Contact Potential Difference (CPD) detection utilizing an in situ Kelvin probe and found to be sensitive to the substrate temperature during film growth, to the substrate temperature during electron irradiation and to the film thickness. Internal electric fields exceeding 108 V/m are developed. It is shown that solid water conducts and stores electrons with “memory” of the film's thermal history. Furthermore, we propose that trapped electrons discharge during substrate annealing in a process that is driven by the formation and propagation of cracks within the molecular layer, similar to the release of gas molecules embedded inside ASW films, at significantly lower temperatures than the onset of crystallization. Thermal binding energies of electrons to the ASW matrix are obtained from the discharge measurements, in the energy range of 0.26±0.08 eV. These values are one order of magnitude smaller than those obtained via photoemission studies.

    更新日期:2018-04-20
  • Au Dendrite Electrocatalysts for CO2 Electrolysis
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Nathan Taylor Nesbitt, Ming Ma, Bartek J Trześniewski, Samantha Jaszewski, Fazel Fallah Tafti, Michael J. Burns, Wilson A. Smith, Michael J. Naughton

    Electrochemical CO2 reduction can convert CO2 into fuels and valuable chemicals using renewable electricity, which provides a prospective path toward large-scale energy storage. Au nanostructured electrodes have demonstrated the best catalytic performance for CO2 conversion: high catalytic selectivity for CO formation at low overpotentials, high current density, and long-term durability. Here, we report selective electrocatalytic CO2 reduction to CO on nanostructured Au with various morphologies, prepared via electrocrystallization with a megahertz potential oscillation. X-ray diffraction showed that the proportion of {100} and {110} to {111} surfaces increased at more negative deposition potentials. Cyclic voltammetry showed the potential of zero charge on a Au film was approximately 0.35 V vs. standard hydrogen electrode (SHE), and that the surface energy decreased by ~1 eV/nm2 at 0.5 V vs. SHE, tending to 0 within several volts in either direction. Scanning electron micrograms showed that the Au crystals grow primarily in the {110} directions. From these data, a model for crystallization from melts was adapted to calculate the roughening temperature of the {111}, {100}, and {110} Miller indices as 7000, 4000, and 1000 K, decreasing for more negative deposition potentials. This offers a framework for exposed facet control in electrocrystallization. In CO2 electrocatalysis, 0.35 V vs. reversible hydrogen electrode was observed to be a turn-on potential for improved CO2 reduction activity; dendrites showed 50% Faradaic efficiency for CO production at more cathodic potentials. The Tafel slope was measured to be 40 mV/decade for {100} and {110}-rich Au dendrites and 110 mV/decade for {111}-dominated Au plates, suggesting the higher surface energy crystal facets may stabilize all the CO2 reduction reaction intermediates.

    更新日期:2018-04-20
  • Work Function Dependence of Vibrational Relaxation Probabilities: NO(v = 2) Scattering from Ultra-Thin Metallic Films of Ag/Au(111)
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Christoph Steinsiek, Pranav R Shirhatti, Jan Geweke, Christof Bartels, Alec M. Wodtke

    We present measurements on the vibrational relaxation of NO(v = 2) scattered from atomically defined thin films of Ag on Au(111). The vibrational relaxation probability is strongly dependent on film thickness, increasing with each of the first three Ag monolayers. We interpret this as the influence of work function which changes with layer thickness. This supports the postulated mechanism of NO vibrational relaxation involving a transient NO- anion.

    更新日期:2018-04-20
  • Molecular Water Adsorption and Reactions on α-Al2O3(0001) and α-Alumina Particles
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Nikolay G Petrik, Patricia L. Huestis, Jay A LaVerne, Alexandr B. Aleksandrov, Thomas M. Orlando, Greg A Kimmel

    The adsorption and reaction of water on single crystal, α-Al2O3(0001) in ultrahigh vacuum, and α-alumina particles in ambient conditions, was investigated using temperature programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), diffuse reflectance infrared Fourier transform spectra (DRIFTS) and other surface science techniques. For a water coverage of 1 H2O/(surface Al3+) on α-Al2O3(0001), no evidence for the surface hydroxyls expected from dissociative adsorption was observed in the infrared spectra, while the ν2 vibration of molecular water was observed. Electron-stimulated desorption of molecular water at low coverages also indicated molecular or mixed (molecular plus dissociative) adsorption. Analysis of Kr TPD spectra showed that the water films wet the alumina substrate and suggested that the films were initially growing layer-by-layer. In contrast with the single crystal results, DRIFTS of water adsorption on alumina particles indicated the presence of surface hydroxyls that persist even after annealing to high temperatures in oxygen. For water on α-Al2O3(0001) at coverages less than 0.3 H2O/(surface Al3+), water desorbed over a broad temperature range extending from ~250 K to 700 K. For larger coverages, water desorption occurred at temperatures between ~160 K and 250 K, consistent with desorption of molecular water. The results, which are consistent with at most a small amount of water dissociation on the Al-terminated (0001) surface, are difficult to reconcile with calculations suggesting that the barrier to dissociation is small. However, the results are consistent with recent vibrational sum frequency experiments showing that the hydroxylation of the Al-terminated (0001) surface takes many days even at ambient pressures and temperatures.

    更新日期:2018-04-20
  • Transferability of CO2 Force Fields for the Prediction of Adsorption Properties in All-Silica Zeolites
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Jian Ren Lim, Chi-Ta Yang, Jihan Kim, Li-Chiang Lin

    We present a systematic and comprehensive investigation of available CO2 force fields for their predictions in adsorption properties in 156 geometrically diverse zeolite structures. The comparison reveals that a large discrepancy in the predicted properties by more than two orders of magnitude may exist. Especially, variation predicted by different force fields appear to be more pronounced for zeolites with more confined pore features, which can be attributed to the repulsive characteristics of force fields. The discrepancy especially impacts zeolites that are deemed to be the best materials for CCS, indicating that the predictions on the best materials can drastically differ based on the choice of force fields. To develop accurate and fully transferable force fields, in this work, we show that the inclusion of adsorption uptake at a high-pressure region (or saturation loading) as well as the diffusion coefficient can be of utmost importance. These properties can be used as indicators to the repulsive behaviors between gas molecules and the framework. Mixture isotherms have also been identified to be potentially useful for the same purpose. Moreover, we have also demonstrated that interaction energies computed using ab initio methods can be useful references to ensure a newly developed force field is capable of describing the energy surface at an atomic level. Overall, the outcomes of this study will be instrumental to the future development of accurate and transferrable force fields, which is critical for future large-scale computational studies.

    更新日期:2018-04-20
  • Thermally Induced Transformation of Non-Hexagonal Carbon Rings in Graphene-like Nanoribbons
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Meizhuang Liu, Mengxi Liu, Zeqi Zha, Jinliang Pan, Xiaohui Qiu, Tao Li, Jiaobing Wang, Yue Zheng, Dingyong Zhong

    Exploring the structural transformation of non-hexagonal rings is of fundamental importance for understanding the thermal stability of non-hexagonal rings and revealing the structure-property relationships. Here, we report on the thermally induced transformation from the fused tetragon-hexagon (4-6) carbon rings to a pair of pentagon (5-5) rings in the graphene-like nanoribbons periodically embedded with tetragon and octagon (4-8-4) carbon rings. A distinct contrast among tetragon, pentagon, hexagon and octagon carbon rings is provided by non-contact atomic force microscopy with atomic resolution. The thermally activated bond rotation with the dissociation of the shared carbon dimer between the 4-6 carbon rings is the key step for the 4-6 to 5-5 transformation. The energy barrier of the bond rotation, which results in the formation of an irregular octagon ring in the transition state, is calculated to be 1.13 eV. The 5-5 defects markedly change the electronic local density of states of the graphene-like nanoribbon, as observed by scanning tunneling microscopy. Our density functional theory calculations indicate that the introduction of periodically embedded 5-5 rings will significantly narrow the electronic band gap of the graphene-like nanoribbons.

    更新日期:2018-04-20
  • Combination of Charge Delocalization and Disorder Enables Efficient Charge Separation at Photoexcited Organic Bilayers
    J. Phys. Chem. C (IF 4.536) Pub Date : 2018-04-19
    Veljko Janković, Nenad Vukmirovic

    We study incoherent charge separation in a lattice model of an all-organic bilayer. Charge delocalization is taken into account by working in the basis of electron-hole pair eigenstates, and the separation is described as a series of incoherent hops between these states. We find that relatively weak energetic disorder, in combination with good charge delocalization, can account for efficient and weakly field- and temperature-dependent separation of the strongly bound charge transfer (CT) state. The separation efficiency is determined by the competition between the recombination from the initial CT state and the escape towards intermediate CT states, from which free-charge states can be reached with certainty. The separation of donor excitons also exhibits quite high yields, less bound excitons separating more efficiently. Overall, our results support the notion that efficient charge separation can be achieved even out of strongly bound pair states without invoking coherent effects.

    更新日期:2018-04-20
  • Structure and Interaction of Nanoparticle-Protein Complexes
    Langmuir (IF 3.833) Pub Date : 2018-04-19
    Sugam Kumar, Indresh Yadav, Vinod Kumar Aswal, Joachim Kohlbrecher

    The integration of nanoparticles with proteins is of high scientific interest due to the amazing potential displayed by their complexes, combining the nanoscale properties of nanoparticles with the specific architectures and functions of the protein molecules. The nanoparticle-protein complexes, in particular, are useful in the emerging field of nanobiotechnology (nanomedicine, drug delivery and biosensors) as the nanoparticles having sizes comparable to that of living cells, can access and operate within the cell. The understanding of nanoparticle interaction with different protein molecules is prerequisite for such applications. The interaction of the two components has shown to result in conformational changes in proteins as well as affect the surface properties and colloidal stability of the nanoparticles. In this feature article, our recent studies, exploring the driving interactions in nanoparticle-protein systems and resultant structures are presented. The anionic colloidal silica nanoparticles and two globular charged proteins [lysozyme and bovine serum albumin (BSA)] have been investigated as model systems. The adsorption behavior of the two proteins on nanoparticles is found to be completely different but they both give rise to similar phase transformation from one-phase to two-phase in respective nanoparticle-protein systems. The presence of protein induces the short-range and long-range attraction between the nanoparticles with lysozyme and BSA, respectively. The observed phase behavior and its dependence on various physiochemical parameters (e.g. nanoparticle size, ionic strength and pH of the solution) have been explained in terms of underlying interactions.

    更新日期:2018-04-20
  • Bifunctionalized redox-responsive layers prepared from a thiolactone copolymer
    Langmuir (IF 3.833) Pub Date : 2018-04-19
    Claire Chattaway, Sabrina Belbekhouche, Filip E Du Prez, Karine Glinel, Sophie Madeleine Demoustier-Champagne

    The development of multifunctional surfaces is of general interest for the fabrication of biomedical, catalytic, microfluidic or biosensing devices. Herein, we report on the preparation of copolymer layers immobilized on gold surface and showing both free thiol and amino groups. These layers are produced by aminolysis of a thiolactone-based copolymer in the presence of a diamine, according to a one-step procedure. The free thiol and amino groups present in the modified copolymer layers can be successfully functionalized with respectively thiolated and carboxylic derivatives, in order to produce bifunctionalized surfaces. In addition, we show that the grafted thiolated derivative can be released by cleavage of the disulfide bond under mild reducing conditions. On the other hand, a side crosslinking reaction occurring during the grafting process and resulting in the formation of copolymer aggregates on the metal surface is evidenced. The methodology developed for the preparation of these bifunctionalized redox-responsive layers should be advantageously used to produce bioactive surfaces with drug loading/release properties.

    更新日期:2018-04-20
  • Circularly Polarized Luminescence from a Pyrene-Cyclodextrin Supra-Dendron
    Langmuir (IF 3.833) Pub Date : 2018-04-19
    Yuening Zhang, Dong Yang, Jianlei Han, Jin Zhou, Qingxian Jin, Minghua Liu, Pengfei Duan

    Soft nanomaterials with circularly polarized luminescence (CPL) have been currently attracting great interests. Here, we report a pyrene-containing π-peptide dendrons hydrogel, which showed 1D and 2D nanostructures with varied CPL activities. It was found that the individual dendron formed hydrogels in a wide pH range (3-12) and self-assembled into helices with pH-tuned pitches. Through chirality transfer, the pyrene unit could show CPL originated from both the monomer and excimer bands. When cyclodextrin was introduced, different supra-dendrons were obtained with β-cyclodextrin (PGAc@β-CD) and γ-cyclodextrin (PGAc@γ-CD) through host-guest interactions, respectively. Interestingly, the PGAc@β-CD and PGAc@γ-CD supra-dendrons self-assembled into 2D nanosheet and entangled nanofibers, respectively, showing cyclodextrin induced circularly polarized emission from both the monomer and excimer bands of pyrene moiety. Thus, through a simple host-guest interaction, both the nanostructures and the chiroptical activities could be modulated

    更新日期:2018-04-20
  • Leidenfrost Self-Rewetting Drops
    J. Phys. Chem. B (IF 3.177) Pub Date : 2018-04-19
    Safouene Ouenzerfi, Souad Harmand, Jesse Schiffler

    As discovered by Leidenfrost, liquids placed on very hot solids levitate on a cushion of their own vapour. This is called also calefaction phenomenon, a dynamical and transient effect, as vapour is injected below the liquid and pressed by the drop weigh. To account the film vapor, we consider the surface tension magnitude as well as the Marangoni effect (in particular the thermal one) which arise with imbalance of surface tension forces. For standard liquids, these forces contribute to amplify the thickness of film layer and the levitation of the droplet. Our findings imply the ability of recent binary mixture liquids , called self-rewetting fluids to reduce the vapour film thickness and demonstrate the powerful influence exerted by different binary mixture to enhance the heat transfer at high temperature. Such self-rewetting fluids are presenting high value of surface tension at high temperature, and in which the Marangoni forces are inversed as from critical temperature. We anticipate our assay to be a way for improvement in the high temperature mass cooling applications.

    更新日期:2018-04-20
  • Effects of CNT size on desalination performance of outer-wall CNT slit membrane
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Elisa Ang Yun Mei, Teng Yong Ng, Jingjie Yeo, Rongming Lin , Zishun Liu, Geethalakshmi K.Rangaswamy

    We investigate the effect of varying carbon nanotube (CNT) size on the desalination performance through slit confinements formed by horizontally aligned CNTs stacked one on top of another. By increasing the CNT size, the results from this study indicate a corresponding increase in water flow rate, accompanied by a slight reduction in salt rejection performance. However, due to the increase in membrane area with CNT size, the permeability performance is observed to reduce as CNT size increases. Nevertheless, a comparison with nanoporous 2D membrane shows that the permeability of the outer-wall CNT slit membrane remains significantly higher for all CNT sizes considered. This indicates that precise dimensions of the CNTs are not highly crucial for achieving ultra-high permeability performance in such membranes, as long as the critical slit size is maintained. In depth analytical studies were further conducted to correlate the influence of curvature effects due to increasing CNT size on the flow characteristcis of the outer-wall CNT membrane. These include the analysis of the measured velocity profiles, oxygen density mapping, potential of mean force profile and friction profile. The present numerical results demonstrates the superb desalination performance of the outer-wall CNT slit membrane, irregardless of the size of CNT use. In addition, the extensive analysis conducted provides a detailed characterization of how curvature affects flow across outer-wall CNT, and can be used to guide future design and fabrication for experimental testing.

    更新日期:2018-04-20
  • 更新日期:2018-04-19
  • Temperature Dependent Rate Coefficients for the Gas-Phase Reaction of the OH Radical with Linear (L2, L3) and Cyclic (D3, D4) Permethylsiloxanes
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    François Bernard, Dimitrios K. Papanastasiou, Vassileios C. Papadimitriou, James B. Burkholder
    更新日期:2018-04-19
  • A Computational and Spectroscopic Analysis of β-Indandione Modified Zinc Porphyrins
    J. Phys. Chem. A (IF 2.847) Pub Date : 2018-04-19
    Joseph I. Mapley, Pawel Wagner, David Leslie Officer, Keith C. Gordon

    Porphyrins have characteristic optical properties which give them potential to be used in a range of applications. In this study a series of β-indandione modified zinc porphyrins, systematically changed in terms of linker length and substituent, resulted in dramatically different absorption spectra than is observed for the parent zinc porphyrin (ZnTXP - 5,10,15,20-tetrakis(3,5-dimethylphenyl)porphyrinato zinc (II)).). These changes included strong absorptions at 420, 541 and 681 nm (110.2, 57.5 and 29.2 mM−1 cm−1, respectively) for the most perturbed compound. Computational studies were conducted and showed the different optical effects are due to a reorganisation of molecular orbitals (MOs) away from Gouterman’s four orbital model. The substituent effects alter both unoccupied and occupied MOs. An increased length of linker group raised the energy of the HOMO-2 such that it plays a significant role in the observed transitions. The degenerate LUMO (eg) set are split by substitution and this splitting may be increased by use of a propylidenodinitrile group which shows the lowest energy transitions and the greatest spectral perturbation from the parent zinc porphyrin complex. These data are supported by resonance Raman spectroscopy studies which show distinct enhancement of phenyl modes for high energy transitions and indandione modes for lower energy transitions.

    更新日期:2018-04-19
  • Ultrafast photochemistry of free-base porphyrin: A theoretical investigation of B → Q internal conversion mediated by dark states
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Konstantin Falahati, Carsten Hamerla, Miquel Huix-Rotllant, Irene Burghardt

    We examine the mechanism of ultrafast internal conversion between the B band (Soret band) and the Q band in porphine (H2P), the prototypical free-base porphyrin, using electronic structure studies and on-the-fly surface-hopping nonadiabatic dynamics. Our study highlights the crucial role of dark states within the N band which are found to mediate B/Q state transfer, necessitating a treatment beyond Gouterman's classic four-orbital model. The sequential B → N → Q pathway dominates largely over the direct B → Q pathway which is found to be energetically unfavorable. Potential energy surface cuts and conical intersections between excited states are determined by TDDFT and validated by CASSCF/CASPT2 and XMCQDPT2 calculations. Both the static analysis and on-the-fly surface-hopping calculations suggest a pathway which involves minor structural deformations via in-plane vibrations. The B → N conversion is a barrierless adiabatic process occurring within ∼20 fs, while the subsequent N → Q conversion occurs via a conical intersection within ∼100 fs, in agreement with time-resolved experiments for porphine and related free base porphyrins. Furthermore, evidence for both sequential and direct transfer to the Qx and Qy states is obtained.

    更新日期:2018-04-19
  • Separation selectivity and structural flexibility of graphene-like 2-dimensional membranes
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Liying Zhang, chao wu, Xiangdong Ding, Yong Fang, Jun Sun

    Single-layer membranes of porous graphene, graphyne derivatives (α/α2/β-graphyne), and porous boron nitride (BN) with similar pore sizes (approximately 8 × 6 Å) have been evaluated for separating pentane isomers using the first-principles calculations. In spite of their slightly bigger pore sizes, graphyne derivatives only allow linear pentane molecules to go through their native pores, while in contrast the porous graphene and BN membranes only block dibranched isomers, i.e., neopentane molecules. Analyses of the geometric changes reveal that the structural flexibility of the membrane determines the penetration barrier. During the penetration of molecules, rigid membranes like graphyne derivatives may exhibit similar distortion like flexible porous graphene and BN, however the energy increase for the former is twice that for the latter. More importantly, the passing molecules experience about two times the geometry distortion and four times energy barrier rise when going through rigid membranes compared with flexible membranes. The more deformed passing molecule and less deformed rigid membrane can result that a much higher penetration barrier. Our results show that the flexibility of porous BN is comparable to porous graphene while graphyne derivatives are much more rigid.

    更新日期:2018-04-19
  • Use multiscale simulation to explore effects of homo-dimerizations between different conformation states on the activation and allosteric pathway for μ-opioid receptor
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Xi Zhang, Yuan Yuan, Longrong Wang, Yanzhi Guo, Menglong Li, Chuan Li, XueMei Pu

    Recently, oligomers of G-protein coupled receptors (GPCRs) have been an important topic in the GPCR fields. However, knowledge about their structures and activation mechanisms have been very limited due to absence of crystal structures. In this work, we used multiscale simulations to study effects of homodimerization between different conformation states on their activations, dynamic behaviors and allosteric communication pathways for μ-OR. The result indicates that the dimerization of one inactive monomer with either one inactive monomer or one active one could enhance its constitutive activation. However, the conformation state of the other protomer (e.g., active or inactive) would influence the activated extent. The dimerization between the two inactive protomers would lead to a negative cooperativity for their activations, which should contribute to the asymmetric activation of GPCR dimers observed by some experiments. On the other hand, for the active monomer, its dimerization with one inactive receptor could alleviate its deactivation, in which the negative and the positive cooperativities are observed between the two subunits of the dimer, depended on different regions. The observation from protein structure network (PSN) analysis indicates that the dimerization of one inactive monomer with one active one would cause a significant drop in the number of main pathways from the ligand binding pocket to the G-protein coupled region for the inactive protomer while the impact is minor for the active protomer. But, for the active monomer or the inactive one, its dimerization with one inactive monomer would significantly changes the types of the residues participating in the pathway with the highest frequency.

    更新日期:2018-04-19
  • Facile preparation of nano-imprinted polymer on magnetite nanoparticles for rapid separation of lead ions from aqueous solution
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Delong Kong, Ning Qiao, Nian Wang, Zhuo Wang, Qi Wang, Zhiyong Zhou, Zhongqi Ren

    A novel nanostructured magnetic ion-imprinted polymer (IIP) was synthesized for the selective adsorption of Pb(II) from aqueous solution. The IIP was prepared on functional Fe3O4@SiO2 core/shell nanoparticles as a support. Monomer units in the polymer featured the typical bidentate ligand itaconic acid. We used ethylene glycol dimethacrylate and 2,2-azoisobisbutyronitrile as a cross-linker and initiator, respectively. The monomers with different acid-base properties and different proportions of cross-linker were investigated to obtain high-performance adsorbents. Our results showed that IIP prepared from itaconic acid had a high adsorption capacity owing to the strong binding between the monomer and Pb(II) template ion. The IIPs were characterized by Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller surface area analysis, thermogravimetric analysis, and transmission electron microscopy. We confirmed the formation of a nano-imprinted shell layer on the surface of Fe3O4@SiO2. The adsorption rate was fast, conforming to a pseudo-second-order kinetic and Langmuir adsorption model; the adsorption mechanism was deemed to be chemisorption as a single molecular layer. The maximum adsorption capacity of the IIP (51.2 mg g−1) was approximately three times as large as that of the non-imprinted polymer (17.9 mg g−1). The selectivity factors for Pb(II) in mixed solutions of Pb (II)/Co(II), Pb (II)/Cu(II), and Pb(II)/Zn(II) were 45.6, 6.45, and 8.3, respectively. Pb-IIP exhibited a high selectivity towards Pb(II), which enabled enrichment of Pb(II) in aqueous solution.

    更新日期:2018-04-19
  • Assessing the scalability of low conductivity substrates for photo-electrodes via modelling of resistive losses
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Isaac Holmes-Gentle, Harsh Agarwal, Faye Alhersh, Klaus Hellgardt

    When scaling up photo-electrochemical processes to larger areas than conventionally studied in the laboratory, substrate performance must be taken into consideration and in this work, a methodology to assess this via an uncomplicated 2 dimensional model is outlined. It highlights that for F-doped SnO2 (FTO), which is ubiquitously used for metal oxide photoanodes, substrate performance becomes significant for moderately sized electrodes (5 cm) under no solar concentration for state of the art Fe2O3 thin films. It is demonstrated that when the process is intensified via solar concentration, current losses become quickly limiting. Methodologies to reduce the impact of substrate ohmic losses are discussed and a new strategy is proposed. Due to the nature of the photo-electrode current-potential relationship, operation at a higher potential where the photo-current saturates (before the dark current is observed) will lead to a minimum in current loss due to substrate performance. Crucially, this work outlines an additional challenge in scaling up photo-electrodes based on low conductivity substrates, and establishes that such challenges are not insurmountable.

    更新日期:2018-04-19
  • The fate of plasma-generated oxygen atoms in aqueous solutions: non-equilibrium atmospheric pressure plasmas as an efficient source of atomic O(aq)
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    J. Benedikt, M. Mokhtar Hefny, A. Shaw, B. R. Buckley, F. Iza, S. Schäkermann, J. E. Bandow
    更新日期:2018-04-19
  • Vibronic relaxation energies of acene-related molecules upon excitation or ionization
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Marcin Andrzejak, Piotr Petelenz

    With perspective of future vibronic studies, ab initio calculations of the energies of vibrational relaxation that follows the processes of singlet or triplet excitation, and positive or negative ionization, are reported for four series of compounds of potential interest in the context of photovoltaic applications, notably those rooted in singlet exciton fission. The commonly used method of evaluating the energy of vibrational relaxation following ionization of an excited molecule is examined and found dubious, especially when used within approaches based on the concept of an effective progression-forming mode. In this regard, methodological consistency in computing the relaxation energies and Franck-Condon parameters for different excitation processes is found to be of paramount importance. The presented results respond to the existing demand for vibronic coupling constants relevant to singlet fission.

    更新日期:2018-04-19
  • Understanding of Deformation Mechanism and Mechanical Characteristics of Cementitious Mineral analogues From First Principles and Reactive Force Field Molecular Dynamics
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Jinyang Jiang, Yiru Yan, Dongshuai Hou, Jiao Yu

    n this paper, the first principle and reactive force field molecular dynamics was utilized to study the mechanical properties of tobermorite 9 Å, tobermorite 11 Å and jennite that are the essential mineral analogues in cement chemistry. The mechanical properties calculated by the first-principle method match well with the previous experimental results, verifying that the introducing of vdW dispersion-type force improves precision efficiently. The calculated elastic constants of the three minerals confirm anisotropic mechanical behavior of the layered structures. The crystal jennite and tobermorite 9 demonstrate stronger ab plane mechanical behavior than the interlayer direction performance due to the stable covalent “dreierketten” silicate chains. For tobermorite 11 Å, the Q3 silicate tetrahedrons, bridging the neighboring calcium silicate sheets, heal the weak interlayer structure and enhance the c-direction stiffness and cohesive strength in great extent. Furthermore, the uniaxial tension test analysis by the reactive force MD elucidated chemical and mechanical responses of the atomic structures in loading resistance. The stress-strain relation of layered mineral tensioned along b direction shows the “strain hardening” region, where stress continues increasing after the yield stage. The strain hardening and ductility enhancement for the minerals are mainly attributed to that silicate chains first de-polymerized into the short chains or separated tetrahedron and then the broken Q species re-polymerize to branch, network structure and ring structure to further resist the loading. Besides, for all three minerals, the proton transferring to the highly reactive oxygen and water dissociating into Si-OH and Ca-OH groups happen during the strain hardening stage, where the Si-O-Si or Si-O-Ca bond starts to break and the calcium atoms and silicate morphology turns to rearrange. The hydrolytic reaction accelerating the structural damage and contributes to weakening of mechanical properties in the interlayer direction. The increasing tensile stress level in the tobermorite 11 Å can contribute to more water dissociation amount.

    更新日期:2018-04-19
  • High Transport and Optical property of Two Dimensional Single-layered Hybrid Perovskite (C4H9NH3)2PbBr4: Theoretical study
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    J H lei, Yu-Qing Zhao, Jianguo Lin, Meng-Qiu Cai, tang q

    The further development of organic-inorganic hybrid perovskites is to pursue high charge carrier mobility and light absorption coefficient. In this paper, we present a detail comparative research of the atomic and electronic structure of single layered perovskites (C4H9NH3)2PbBr4 with two dimensional/three dimensional(2D/3D) spatial arrangement to predict the charge carrier mobility in plane along with charge effective mass, elastic constant, and deformation potential. The calculated results reveal that the intrinsic carrier mobilities of 2D single layer hybrid perovskite(C4H9NH3)2PbBr4 in plane along <100> and <010> directions are more superior than that of 3D structure. Furthermore the optical properties are calculated from the electronic structure, it is found that the light absorption spectrum of 2D single layered perovskite (C4H9NH3)2PbBr4 with high absorption coefficient is wider than that of 3D phase. We speculate the superior mobility and wider absorption spectrum in 2D mono-layered perovskite are traced to denser charge density and ferroelectricity originated from the structure distortion upon 3D-to-2D structure transformation. These results indicate that the 2D single layered hybrid perovskite (C4H9NH3)2PbBr4 is a potential candidate for the application in the optoelectronic and photovoltaic field.

    更新日期:2018-04-19
  • Modeling TADF in Organic Emitters Requires a Careful Consideration of the Environment and Going Beyond the Franck-Condon Approximation
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Jan-Michael Mewes

    The origin of the thermally-activated delayed fluorescence (TADF) of three organic emitters is investigated, focusing on the nature of the lowest excited states, their transition properties, as well as the role of the environment. For this purpose, the algebraic-diagrammatic construction for the polarization propagator at second order of perturbation theory [ADC(2)], time-dependent density-functional theory in the Tamm-Dancoff approximation (TDA) and unrestricted Kohn-Sham DFT in combination with the maximum-overlap method (ΔDFT) are employed. The influence of the dielectric environment is rigorously included using different variants of the polarizable continuum model. The calculations reveal the lowest excited singlet and triplet states of all studied emitters to be dominated by charge-transfer (CT) character already in the most apolar environment corresponding to cyclohexane. This entails a drastic reduction of the singlet-triplet gaps, increasing the calculated TADF rates by several orders of magnitude. Another ingredient for accurate TADF rates is hidden in the excited-state potential-energy surfaces along the donor-acceptor twisting angle. A presence of large shallow plateaus in apolar environments causes the transition properties to be governed by thermal fluctuations rather than the minimum-energy geometries. This leads to a large increase of the oscillator strengths, as well as a breakdown of the Franck-Condon approximation. The last ingredient is a small but significant spin-orbit coupling (SOC) between the singlet and triplet CT states, which is traced back to a delocalization of the excitation hole or excited electron of the triplet CT state. Taking into account all of these effects, a reasonable agreement with experimental TADF and fluorescence lifetimes is obtained. For this, it proves to be sufficient to consider only the lowest lying singlet and triplet states.

    更新日期:2018-04-19
  • Membrane Deformation Induces Clustering of Norovirus Bound to Glycosphingolipids in a Supported Cell-Membrane Mimic
    J. Phys. Chem. Lett. (IF 9.353) Pub Date : 2018-04-19
    Nagma Parveen, Inga Rimkute, Stephan Block, Gustaf E. Rydell, Daniel Midtvedt, Göran Larson, Vesa P. Hytönen, Vladimir P. Zhdanov, Anders Lundgren, Fredrik Höök
    更新日期:2018-04-19
  • Static second hyperpolarizability of inverse sandwich compounds (M1-C5H5-M2) of alkali (M1=Li, Na, K) and alkaline earth metals (M2= Be, Mg, Ca)
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Kaushik Hatua, Avijit Mondal , Prasanta K. Nandi

    In the investigated inverse sandwich complexes charge transfer from alkali metal (M1) leads to aromatically stabilized Cp ring which prevents further charge transfer from the alkaline earth metal (M2). This electron push effect results in diffuse electron density from the outermost “ns” subshell of alkaline earth metal. The later is weakly bound to the alkali metal-C5H5 complex. The vertical ionization energy of chosen M1-Cp-M2 complexes are smaller than the corresponding alkaline earth metals. Large second hyperpolarizability (106 - 108 au) has been obtained for the studied molecules. The correction due to the basis set superposition error (BSSE) in the calculated second hyperpolarizability has been found to be small for larger systems while it is rather significant for small systems. The MP4SDQ and CCSD results show a fair agreement which indicates the necessity of higher order electron correlation treatment in the accurate description of second hyperpolarizability. Calculated dynamic second hyperpolarizabilities at 1064 nm are found to increase considerably for most of the chosen metal complexes.

    更新日期:2018-04-19
  • Hematite/Silica Nanoparticle Bilayers at Mica: AFM and Electrokinetic Characteristics
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-19
    Maria Morga, Zbigniew Adamczyk, Dominik Kosior, Magdalena Oćwieja

    Quantitative studies on self-assembled hematite/silica nanoparticle (NP) bilayers at mica were performed applying scanning electron microscopy (SEM), atomic force microscopy (AFM), and streaming potential measurements. The coverage of the supporting hematite layer was adjusted changing the bulk concentration of the suspension and the deposition time. The coverage was determined by a direct enumeration of deposited particles from AFM images and SEM micrographs. Afterward, silica nanoparticle monolayers were assembled under the diffusion-controlled transport. A unique functional relationship was derived connecting the silica coverage with the hematite precursor layer coverage. The formation of the hematite monolayer and the hematite/silica bilayer was also monitored in situ by streaming potential measurements. It was confirmed that the zeta potential of bilayers was independent of the supporting layer coverage exceeding 0.15. These measurements were theoretically interpreted in terms of a general electrokinetic model that allowed one to specify a formula for calculating nanoparticle coverages in the bilayers. Additionally, performing the desorption experiments, the interactions among the hematite/silica particles in the bilayers were interpreted in terms of DLVO interactions among particles. These results may facilitate developing a robust method of preparing nanoparticle bilayers of controlled properties, having potential applications in catalytic processes or for constructing biointerfaces.

    更新日期:2018-04-19
  • 更新日期:2018-04-19
  • A novel nonlinear nano-scale wear law for metallic brake pads
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-12
    Sandeep P. Patil, Sri Harsha Chilakamarri, Bernd Markert
    更新日期:2018-04-19
  • Infrared laser dissociation of single megadalton polymer ions in a gated electrostatic ion trap: the added value of statistical analysis of individual events
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-12
    Mohammad A. Halim, Christian Clavier, Xavier Dagany, Michel Kerleroux, Philippe Dugourd, Robert C. Dunbar, Rodolphe Antoine
    更新日期:2018-04-19
  • Magnetization relaxation in the single-ion magnet DySc2N@C80: quantum tunneling, magnetic dilution, and unconventional temperature dependence
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-10
    D. S. Krylov, F. Liu, A. Brandenburg, L. Spree, V. Bon, S. Kaskel, A. U. B. Wolter, B. Büchner, S. M. Avdoshenko, A. A. Popov
    更新日期:2018-04-19
  • 更新日期:2018-04-19
  • Application of far-infrared spectroscopy to the structural identification of protein materials
    Phys. Chem. Chem. Phys. (IF 4.123) Pub Date : 2018-04-04
    Yanchen Han, Shengjie Ling, Zeming Qi, Zhengzhong Shao, Xin Chen
    更新日期:2018-04-19
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
化学 • 材料 期刊列表