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C-H—O interactions of a self-assembled triple helix based on the 1-acetamido-3(2-pyrazinyl)-imidazolium cation has been probed by high pressure. The infrared spectroscopic profiles and ab initio calculations allow us to make a vibrational assignment of this compound. The C-H bonds forming C-H—O interactions shorten as the pressure was elevated, while free C-H vibration modes show low sensitivity to high pressure. The pressure-dependent results can be attributed to the strengthening of C-H—O electrostatic-dispersion interactions upon increasing pressure. The appearance of the free-NH infrared absorption indicates that the conventional NH—O hydrogen bond does not dominate the inter-strand packing in the compound. It is proposed that the charge-enhanced C-H—O interactions, forming a helical hydrogen-bonding network, disturb the formation of inter-strand N-H—O hydrogen-bonding in order to form a maximum number of hydrogen bonds. Applying high-pressure seems not to change the C=O bond length in contrast to the trend of blue-shift in frequency of C-H vibrations. London dispersion energy is suggested to be required for understanding the pressure-dependent results, although more additional terms, such as the effect in the presence of charge, are needed for the correct explanation. This work demonstrates that high-pressure studies may have the potential to provide insight into the C-H—O structural properties of biological related systems. [ABSTRACT FROM AUTHOR]

Increasing the stability of perovskite solar cells is one of the most important tasks in the photovoltaic industry. Thus, the structural, energetic, and electronic properties of pure CH3NH3PbI3 and fully doped compounds (CH3NH3PbBr3 and CH3NH3PbCl3) in cubic and tetragonal phases were investigated using density functional theory calculations. We also considered the effects of mixed halide perovskites CH3NH3PbI2X (where X = Br and Cl) and compared their properties with CH3NH3PbI3. The DFT results indicate that the phase transformation from tetragonal to cubic phase decreases the band gap. The calculated results show that the X‐site ion plays a vital role in the geometrical stability and electronic levels. An increase in the band gap and a reduction in the lattice constants are more apparent in CH3NH3PbI2X compounds (I > Br > Cl). [ABSTRACT FROM AUTHOR]

Highlights • Sensing properties of dopamine on pure SWNT and B,N co-doped SWNT. • Dopamine on pure SWNT will not obviously change the conductivity of SWNT. • It forms an N DA B dative bond to enhance dopamine sensing on B,N co-doped SWNT. • N DA B dative bond causes significant conductivity changes of B,N co-doped SWNT. Abstract Dopamine (DA) is a catecholamine neurotransmitter that can cause some nervous system disorders, leading to Parkinson's disease. Thus, the development of a dopamine sensor is important for the diagnosis of these disorders. Here, we studied the adsorption of DA on semiconducting single-walled carbon nanotubes (SWNTs), including pure, and B,N co-doped (6,5) SWNTs, via DFT calculations. Our results indicated that DA can form multiple molecular interactions with pure (6,5) SWNT. However, these interactions have limited effects on the electronic properties; therefore, the band gap and conductivity of pure (6,5) SWNT did not change significantly after DA adsorption. On the other hand, regarding the adsorption of DA on a B,N co-doped (6,5) SWNT, we found that not only stronger molecular interactions such as C-H⋯π interactions were established but also an N DA B dative bond between DA and the SWNT was formed, altering the electronic properties of this SWNT. These cooperative interactions after DA adsorption caused much more pronounced changes in the band gaps and conductivities of B,N co-doped (6,5) SWNTs than in those of pure (6,5) SWNT. Our results demonstrated that the sensitivity of a pure (6,5) SWNT to detect dopamine was enhanced in the B,N co-doped (6,5) SWNT. [ABSTRACT FROM AUTHOR]

The quality of the SEI layer was improved through the synergistic effect of fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPF) dual additives. [Display omitted] • Role of dual additives (FEC and LiPF) on the electrolyte reactivity with Li metal anodes is analyzed. • Synergistic effects of dual additives on SEI formation mechanisms are explored. • Atomic charges are used to predict the representative F 1s XPS and confirmed experimentally identified SEI components. • Constructive suggestions have been proposed for improving SEI quality. Improving the quality of the solid-electrolyte interphase (SEI) layer is highly imperative to stabilize the Li-metal anodes for the practical application of high-energy–density batteries. However, controllably managing the formation of robust SEI layers on the anode is challenging in state-of-the-art electrolytes. Herein, we discuss the role of dual additives fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO 2 F 2 , LiPF) within the commercial electrolyte mixture (LiPF 6 /EC/DEC) considering their reactivity with Li metal anodes using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Synergistic effects of dual additives on SEI formation mechanisms are explored systematically by invoking different electrolyte mixtures including pure electrolyte (LP47), mono-additive (LP47/FEC and LP47/LiPF), and dual additives (LP47/FEC/LiPF). The present work suggests that the addition of dual additives accelerates the reduction of salt and additives while increasing the formation of a LiF-rich SEI layer. In addition, calculated atomic charges are applied to predict the representative F 1s X-ray photoelectron (XPS) signal, and our results agree well with the experimentally identified SEI components. The nature of carbon and oxygen-containing groups resulting from the electrolyte decompositions at the anode surface is also analyzed. We find that the presence of dual additives inhibits undesirable solvent degradation in the respective mixtures, which effectively restricts the hazardous side products at the electrolyte-anode interface and improves SEI layer quality. [ABSTRACT FROM AUTHOR]

Elucidating the complex degradation pathways and formed decomposition products of the electrolytes in Li-metal batteries remains challenging. So far, computational studies have been dominated by studying the reactions at inert Li-metal surfaces. In contrast, this study combines DFT and AIMD calculations to explore the Li-nucleation process for studying interfacial reactions during Li-plating by introducing Li-atoms close to the metal surface. These Li-atoms were added into the PEO polymer electrolytes in three stages to simulate the spontaneous reactions. It is found that the highly reactive Li-atoms added during the simulated nucleation contribute to PEO decomposition, and the resulting SEI components in this calculation include lithium alkoxide, ethylene, and lithium ethylene complexes. Meanwhile, the analysis of atomic charge provides a reliable guideline for XPS spectrum fitting in these complicated multicomponent systems. This work gives new insights into the Li-nucleation process, and experimental XPS data supporting this computational strategy. The AIMD/DFT approach combined with surface XPS spectra can thus help efficiently screen potential polymer materials for solid-state battery polymer electrolytes. [ABSTRACT FROM AUTHOR]

• The transition from CO 2 physisorption to chemisorption had a lower free energy barrier. • HCOOH and CH 3 OH were produced effectively on the monoclinic Bi 2 O 3 surface. • COOH path exhibited a lower free energy barrier for CO 2 RR. • The microkinetic predicts the desorption temperature for the particular product. To date, the electrochemical reduction of CO 2 (CO 2 RR) into valuable chemicals is a promising method for combating global warming. However, finding a suitable electrocatalyst for CO 2 RR is critical to reducing CO 2 emissions. Herein, the CO 2 RR mechanism on a pristine monoclinic Bi 2 O 3 (120) surface was thoroughly investigated using density-functional theory (DFT) calculations. The CO 2 adsorption modes of side-on, end-on, and chemisorbed were compared, with the chemisorbed species outperforming for CO 2 activation. Furthermore, analyses of the Bader charge, the density of states, and electron density difference strongly suggest that the Bi 2 O 3 (120) surface has excellent activation for CO 2 molecules. More importantly, the DFT calculations revealed that the electrochemical CO 2 RR over the Bi 2 O 3 surface favors both formic acid and methanol in the limiting-potential step of *CO 2 → *COOH with the free energy barriers of 0.86 eV and 0.87 eV with and without solvent, respectively. The microkinetic simulation also supports the DFT result, showing the possibility of more selective production by predicting desorption temperatures. This research suggests a promising way for CO 2 RR mechanisms on pristine monoclinic Bi 2 O 3 surfaces to produce formic acid (HCOOH) and methanol (CH 3 OH). [Display omitted] [ABSTRACT FROM AUTHOR]

The ability of the polymer‐based graphitic carbon nitride (g‐C3N4) as a gas sensor toward NO, NO2, CO, CO2, SO2, SO3, and O2 gasses is assessed using density functional theory (DFT) calculations in terms of energetic and electronic transport characteristics. In particular, this study is aimed to explore the role of zigzag and armchair edges of the g‐C3N4 sheet on sensing performances. The electronic properties of adsorption systems, such as Bader charge analysis, band gaps, work function, and density of states (DOS), are used to understand the interaction between the adsorbed gas molecules and the g‐C3N4 sheet. Our calculated results indicate that SOx (SO3 and SO2) gasses have higher adsorption energies on the g‐C3N4 sheet than other gasses. Furthermore, the transport properties, such as current–voltage (I‐V) and resistance‐voltage (R‐V) curves along the zigzag and armchair directions are calculated using the non‐equilibrium Green's function (NEGF) method to understand the performance of the g‐C3N4 sheet as a prominent conductive/resistive sensor. The I‐V/R‐V results indicate that the zigzag g‐C3N4 sheet has excellent sensing ability toward SOx gasses at low applied voltages. However, the presence of H2O degrades the sensing performance of the armchair g‐C3N4 sheet. Theoretical recovery time has also been calculated to evaluate the reusability of g‐C3N4 sheet‐based gas sensors. Our results reveal that the zigzag g‐C3N4 sheet‐based sensing device has a remarkably high sensitivity (>300%) and selectivity toward SOx gasses and has the potential to work in a complex environment. [ABSTRACT FROM AUTHOR]

Conversion of CO 2 to chemicals and fuels has attracted considerable attention as CO 2 is a nontoxic, non-flammable, and cheap carbon-oxygen source. However, the kinetics of CO 2 conversion into other chemicals remains a challenge due to its thermodynamic stability. Herein, P and S co-doped graphitic-carbon nitride (PSCN) catalyst was synthesized through one-step thermal condensation to improve its Lewis acidity and basicity and investigate carbon dioxide/glycerol (CO 2 /GLY) conversion. The catalytic GLY conversion at 210 °C reached 60% and 85% using pristine g-C 3 N 4 (CN) and PSCN, respectively, with CO 2 as a carbon feedstock and CH 3 CN as a dehydrating agent. Density-functional theory (DFT) calculations revealed that the efficient charge transfer resulting from P and S doping could increase the catalytic activity for CO 2 /GLY conversion by lowering the activation barrier. This is the first study to demonstrate the catalytic activity of the PSCN catalyst for the CO 2 /GLY conversion and the computational work for the GLY carboxylation reaction. Moreover, the interaction site and adsorption energy were investigated for the adsorption of CO 2 and GLY on PSCN and CN to elucidate the reaction mechanism. Our results demonstrated that PSCN could serve as a superior catalyst and pave new light for CO 2 /GLY conversion. [Display omitted] • P and S co-doped g-C 3 N 4 (PSCN) catalyst was prepared for a catalytic CO 2 /glycerol reaction. • PSCN exhibited a conversion of 85% at 210 °C because of its enhanced Lewis acidity and basicity. • PSCN decreased the energy barrier and improved the co-adsorption and glycerol carboxylation. [ABSTRACT FROM AUTHOR]

Mixed alkyl carbonates are widely used as solvent for a various lithium-ion battery applications. Understanding the behavior of each solvent in the mixed system is crucial for controlling the electrolyte composition. In this paper, we report a systematic electrochemical and spectroscopic comparison of the reduction of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) when used as single (PC), binary (EC/PC, EC/DEC), and ternary (EC/PC/DEC) solvent systems. The reduction products are identified based on Fourier transform infrared spectroscopy (FTIR) after employing linear sweep voltammetry to certain potential regions and their possible formation mechanisms are discussed. FTIR analyses revealed that the reduction of EC and PC was not considerably influenced by the presence of other alkyl carbonates. However, DEC exhibited a different reduction product when used in EC/DEC and EC/PC/DEC solvent systems. The reduction of EC occurred before that of PC and DEC and produced a passivating surface film that prevented carbon exfoliation caused by PC. Battery performance test, cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscope is employed to study the surface films formed. The binary EC/DEC solvent system demonstrated more favorable performance, smaller impedance, and higher Li+ ion diffusivity than did the other solvent systems used in this study. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogen storage capacity of transition metal (TM) decorated boron (B) doped graphene surface through spill over mechanism have been studied using first principle calculations. Here we propose a new strategy to increase the hydrogen storage in the B-doped graphene surface. We decorated the surface with different TM atoms with different binding energy strengths in order to enrich both adsorption as well as desorption of hydrogen at ambient conditions. We find that among the considered TM atoms, the Ni, Pd and Co atoms are suitable for decorating B-doped graphene surface, which can be adsorbed stably on the surface. Our results show that the activation energies for H atom diffusion are much smaller than the previously reported values, indicating that a fast H diffusion on this proposed surface can be achieved. Further, the desorption energy of hydrogen on the Co is between 0.49 and 1.3eV/molecule, which is close to the energies required to obtain reversible storage at room temperature. [Copyright &y& Elsevier]

Abstract: Combining experimental and computational techniques can provide a better understanding of surface film formation processes that occur in the lithium-ion battery. In this paper, we show that this joint approach can provide a mechanistic understanding of the effect of oxygen in the reduction of propylene carbonate (PC). We perform FTIR analysis, inside a glove box, after conducting linear sweep voltammetry (LSV) from an open-circuit voltage (OCV) to selected potential regions; subtraction between two successive IR spectra has been made to identify the reduction products formed within each potential range. FTIR analysis in the potential range from OCV to −0.1 V, in conjunction with density functional theory (DFT) calculations, confirm the formation of solvated Li2CO3 and (PC)2LiOC(O)OCH(CH3)CH2OLi(PC) due to PC reduction. Our experimental results and DFT calculations suggest that in the potential range from OCV to 1.6 V, PC, in the presence of O2, can easily decompose by the superoxide ion through a nucleophilic attack at the ethereal carbon atom. [Copyright &y& Elsevier]

[Display omitted] • Ir/TiO 2 catalyst is prepared and studied CH 4 activation and its steam reforming. • 2 wt% Ir/TiO 2 catalyst exhibits low activation barrier and high TOF. • DFT results support the low-temperature activity of small Ir clusters for SRM. • Predicted product temperature with microkinetics agrees well with the experiment. Hydrogen production via low-temperature (<550 °C) steam reforming of methane (SRM) has attracted increasing research attention due to its importance as an alternative, efficient, and environmentally benign energy carrier. The thermodynamic limitation of low-temperature SRM can be eased by process design such as using a membrane reactor or an adsorption-enhanced reforming process, and an active low-temperature SRM catalyst with high stability would be indispensable. Herein, we report a 2 wt% Ir/TiO 2 catalyst that exhibits high methane conversion activity in low-temperature SRM with a relatively high turnover frequency (TOF) and a low activation energy in comparison with the literature. Long-term catalyst stability test demonstrates a good resistance to coking and sintering during low-temperature SRM reactions. In situ spectroscopy analyses and density functional theory (DFT) calculations reveal that the small Ir clusters and Ir single atoms (SAs) are both active for methane conversion, while the clusters exhibit higher activity than SAs for low-temperature SRM reaction. Microkinetic simulation based on DFT calculations shows consistent product formation temperatures and the simulation nicely reproduces the product distribution observed in experimental analysis, which confirms the superior SRM activity of the TiO 2 -supported Ir clusters in this work. [ABSTRACT FROM AUTHOR]

Abstract: A series of novel organosoluble polyimides and copolyimides with a propeller-shaped triarylamine unit were prepared from diamine and various aromatic dianhydrides via direct polycondensation. All of the polymers possessed tough, flexible, and strong films with high molecular weights. The polyimide and copolyimide films revealed electrochromic characteristics, with a color change from pale yellowish at its neutral state, to green, and finally to blue at its oxidized state, at applied potentials ranging from 0 to 1.50 V. The polyimide (Ib) film exhibited switching times of 4.5 s at 1.08 V at 424 and 877 nm and 1.9 s for fast bleaching due to a pendent substituted 2-phenyl-2-isopropyl group. Cyclic voltammetry (CV) of the polymer films showed two reversible redox couples at potentials of 0.91–0.99 V and 1.30–1.38 V, respectively. The CV results of the model compound M1 and model polyimide M2, were not a match to the oxidation peaks of polyimide Ib, indicating that the contribution of the oxidation was not only from the electron removal of nitrogen atoms. [Copyright &y& Elsevier]

Abstract: SiH4 and GeH4 dissociative adsorptions on a buckled SiGe(100)-2×1 surface have been analyzed using density functional theory (DFT) at the B3LYP level. The Ge alloying in the Si(100)-2×1 surface affects the dimer buckling and its surface reactivity. Systematic Ge influences on the reaction energetics are found in SiH4 and GeH4 reactions with four dimers of Si∗–Si, Ge∗–Si, Ge∗–Ge, and Si∗–Ge (∗ denotes the protruded atom). On a half H-covered surface, the energy barriers for silane and germane adsorption are higher than those on the pristine surface. The energy barrier for silane adsorption is higher than the corresponding barrier for germane adsorption. Rate constants are also calculated using the transition-state theory. We conclude that the SiGe surface reactivity in adsorption reaction depends on the Ge presence in dimer form. If the surface Ge is present in form of Ge∗–Ge, the surface reactivity decreases as the Ge∗–Ge content increases. If the surface Ge prefers to be in form of Ge∗–Si at low Ge contents, the surface reactivity increases first, then decreases at high Ge surface contents when Ge∗–Ge prevails. The calculated rate constant ratio of GeH4 adsorption on Si∗–Si over Ge∗–Ge at 650°C is 2.1, which agrees with the experimental ratio of GeH4 adsorption probability on Si(100) over Si(100) covered by one monolayer Ge. The experimental ratio is 1.7 measured through supersonic molecular beam techniques. This consistency between calculation and experimental results supports that one monolayer of Ge on Si(100) exists in form of Ge∗–Ge dimer. [Copyright &y& Elsevier]

Abstract: Quantum chemical calculations of the gas-phase reactions of tertiarybutylhydrazine ((CH3)3CNHNH2) were performed to understand the possible reaction path when used as a nitrogen source for gallium nitride film growth. Thermochemical prediction using density functional theory showed that the reaction to form hydrazine (N2H4) and isobutene ((CH3)2CCH2) through β-hydride elimination in the tertiarybutyl ligand has the lowest activation energy barrier of 63 kcal/mol. In addition, rate constants calculations using transition-state theory also showed that the β-hydride elimination reaction predominated over all other gas-phase reaction paths. The calculated thermochemical and kinetic results agreed very well with the reported pyrolysis data. [Copyright &y& Elsevier]

The NH4+(NH3)n [n=0–6] clusters have been studied using ab initio calculations. For n=0 and 1, the geometry of clusters are optimized at B3LYP, MP2, CCD and QCISD levels with several basis sets, and the binding energies are compared to experimental results to find the reliable and less computationally demanding methods for the calculations of larger clusters. For n=2–6, the geometry optimizations and NH stretching vibrational spectra are performed at B3LYP and MP2 levels with 6-31+G* basis set. The binding energies are corrected by basis set superposition errors (BSSE) and zero-point vibrational energies (ZPVE). These two approaches that correspondingly predict the filled first solvation shell are the lowest in energies at n=1–4. The vibrational frequency shift of ammonium molecules have been investigated along with the frequency characteristics depending on the presence/absence of outer-shell ammonia molecules. In this study, the calculated binding energies and the characteristic NH stretching vibrational frequency shift are in good agreement with experimental data. In addition, the barriers of proton transfer between two heavy atoms and the internal rotation of ammonia molecular along the NH axis in NH4+(NH3)n are estimated with several levels. [Copyright &y& Elsevier]

• Chlorobenzene can only be physisorbed on pristine SWCNT and BNNT. • Doping Al to SWCNT and BNNT increase the E ads of CB by forming an Al Cl dative bond. • The sensitivity of Al-doped BNNT to chlorobenzene is better than that of Al-doped SWCNT. Chlorobenzene (CB) is a harmful, aromatic volatile organic compound and has been demonstrated to be a primary precursor of dioxin formation in industrial processes. Single-walled carbon nanotubes (SWCNT) and boron nitride nanotubes (BNNT) have attracted tremendous attention in a wide range of applications, including chemical gas sensors. In this work, we studied the sensing behavior of both semiconducting (8, 0) SWCNT and BNNT via aluminum doping by using DFT calculations. Our results reveal that CB can only adsorb on pristine SWCNT and BNNT via physisorption, while the Al-doped nanotubes greatly enhance the adsorption energies of the CB molecule. This is caused by the electron donating from the Cl atom to the Al atom to form an Al Cl dative bond. The strong interaction caused by this Al Cl dative bond formation leads to the breaking of the partial-double-bond characteristic of the C Cl bond of the CB molecule so that the adsorption energies of CB can be enhanced. Moreover, we also found that Al-doped (8,0) BNNT displays a huge conductivity increase because of the considerable change in the band gap value after detecting the CB molecule. Our results imply that the Al-doped nanotubes, especially Al-doped BNNT, might be highly sensitive to chlorine-containing species. [ABSTRACT FROM AUTHOR]

Wettability is a key property of single-walled carbon nanotubes (SWNTs), governed both by the chemical composition and geometrical microstructure of the contact surface. Wettability of SWNTs can be enhanced via doping with heteroatoms such as boron or nitrogen to tune the electronic properties of SWNTs. We investigated the adsorption of the water monomer and dimer on pristine and B-doped (5,5) SWNTs by first-principles calculations. The calculated adsorption energy of the water monomer and dimer on pristine (5,5) SWNTs was low. The water dimer can form B O dative bonds with B-doped (5,5) SWNTs, enhancing interactions among each other. A higher adsorption energy of the water dimer was obtained with higher B-doping concentration. Additionally, electronic property analysis showed electron transfer from the water dimer to the boron of the SWNT, forming a B O dative bond, then from the SWNT to the water dimer through an OH⋯π interaction. The interactions between water dimer and SWNT are strongly cooperative. We further compared the adsorption energies of the water dimer and trimer on B-doped SWNTs with their cohesive energies. The adsorption energies increase due to cooperative effects, thereby enhancing wettability. We can expect that B-doped SWNTs can efficiently improve the wettability of carbon nanotubes. Unlabelled Image • Water dimer has larger adsorption energy than water monomer on pure SWNT and B-SWNT. • The higher the boron-doping contents the larger adsorption energy of the water dimer. • The cooperative effect between water dimer and B-SWNT causes a big adsorption energy. • Boron-doping can efficiently improve the wettability of SWNT. [ABSTRACT FROM AUTHOR]

• IrO 2 nanoparticles of around 7 nm are found to activate CH 4 at temperatures as low as −115 °C. • IrO 2 nanoparticles show higher CH 4 activation activity than reduced Ir nanoparticles. • DFT modeling demonstrates contribution of highly active IrO 2 (1 1 0) and (2 1 1) facets to the CH 4 activation. • Oxidation state of Ir is a governing factor determining the CH 4 activation activity. Iridium oxide (IrO 2) shows a good potential for CH 4 activation at mild conditions evidenced by density functional theory (DFT) and surface science studies. In this study, IrO 2 NP (nanoparticles) of around 7 nm are found to activate CH 4 at a temperature as low as −110 °C when Raman bands of surface species at 1328 and 1581 cm−1 are observed, accompanied by the partial reduction of IrO 2. DFT modeling of methane activation on IrO 2 indicates that CH 3 , CH 2 O br , H 2 O br , and HO br (O br , bridging oxygen between two Ir) are the more abundance surface species and the calculated vibrational frequencies of these species consistently explain the observed results of in situ Raman and in situ DRIFTS. The CH 4 activation temperature on Ir NP of around 5.4 nm is found nearly 200 °C higher than that over IrO 2 NP, confirming the superior activity of IrO 2. DFT modeling demonstrates the high CH 4 reactivity over IrO 2 (2 1 1) and the even higher activity of partially reduced IrO 2. This evidences the important role of the oxidation state of Ir in determining the catalytic activity and it implies that tuning Ir oxidation state and/or designing Ir-oxide interface may facilitate the fabrication of value-added chemicals from methane over iridium-based catalysts. [ABSTRACT FROM AUTHOR]

Methane conversion by using transition metal catalysts plays in an important role in various usages of the industrial process. The mechanism of methane conversion on B, N‐co‐doped graphene supported Ir and Pt clusters, BNG‐Ir4 and BNG‐Pt4, have been investigated using density functional theory calculations. Methane was found to adsorb on BNG‐Ir4 and BNG‐Pt4 clusters via strong agostic interactions. The first step of methane dehydrogenation on BNG‐Ir4 has a lower energy barrier, indicating a facile methane dissociation on BNG‐Ir4. In addition, it shows that hydrogen molecule can form on the BNG‐Ir4 and hydrogen can desorb from the surface. Besides, the C‐C coupling reaction of CH3 to form ethane is a more thermodynamically favorable process than CH3 dehydrogenation on BNG‐Ir4. Further, ethane is easier to desorb from the surface due to its low desorption energy. Therefore, the BNG‐Ir4 cluster is a potential catalyst for activating methane to form ethane and to produce hydrogen. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This paper describes a systematic study on the clathrate structure of H+(H2O)21 using tandem mass spectrometry, vibrational predissociation spectroscopy, Monte Carlo simulations, and density functional theory calculations. We produced H+(H2O)n from a continuous corona-discharged supersonic expansion and observed three anomalies simultaneously at the cluster temperature near 150 K, including (1) the peak at n=21 is more intense than its neighboring ions in the mass spectrum, (2) the size-dependent dissociation fractions show a distinct drop for the 21-mer, and (3) the infrared spectrum of H+(H2O)21 exhibits only a single feature at 3699 cm-1, corresponding to the free-OH stretching of three-coordinated water molecules. Interestingly, the anomalies appear or disappear together with cluster temperature, indicating close correlation of these three observations. The observations, together with Monte Carlo simulations and density functional theory calculations, corroborate the notion for the formation of a distorted pentagonal dodecahedral (512) cage with a H2O molecule in the cage and a H3O+ ion on the surface for this “magic number” water cluster ion. The dodecahedral cage melts at higher temperatures, as evidenced by the emergence of a free-OH stretching feature at 3717 cm-1 for the two-coordinated water in H+(H2O)21 produced in a warmer molecular beam. Extension of this study to larger clusters strongly suggests that the experimentally observed isomer of H+(H2O)28 is most likely to consist of a distorted protonated pentakaidecahedral (51263) cage enclosing two neutral water molecules. [ABSTRACT FROM AUTHOR]

[Display omitted] • The catalytic activity of Au clusters supported on BN surface is explored. • Role of water on the CO oxidation mechanism is investigated. • Presence of water molecule weakens CO adsorption and readily activates O 2. • BN support eases the overall CO oxidation on pyramid type Au clusters. The catalytic role of water and the hexagonal boron nitride (BN) support on the CO oxidation mechanism over Au 9 cluster have been systematically investigated using density functional theory calculations. It is demonstrated that the presence of water molecule weakens the CO adsorption on Au 9 /BN surface, which is relative to the water molecule concentration. It is found that the key role of the water molecule in CO oxidation is to activate O 2 and favors the formation of HO 2 and COOH species on Au 9 /BN surface with very low reaction barriers. Our results indicate that the support BN surface alters the charge state of the Au cluster, which assist the overall CO oxidation. Further, the observed blue shift in the CO stretching frequency in the presence of water molecules validates the experimental study of CO oxidation in Au/BN catalyst. The calculated reaction barriers for CO oxidation via both HO 2 and COOH species are not more than 0.28 eV, shows that Au 9 /BN surface will be a good catalyst for CO oxidation at ambient environment. [ABSTRACT FROM AUTHOR]

The interlayer hydrogen-bonded, uniform, and spherical covalent organic frameworks (USCOFs) and non-hydrogen bonded, and spherical covalent organic polymers (USCOPs) were synthesized in a series of aromatic and nonaromatic solvents at room temperature. The presence of interlayer hydrogen bonds between USCOFs were investigated via electron density difference (EDD) and stacking energy calculation in various solvents by DFT methods. The in-situ mid-angle X-ray scattering measurements indicate that the (100)-plane at 0.33 Å continuously grows in USCOFs, which was absent in USCOPs. The crystalline USCOFs exhibit a high surface area of 658 m2g−1, with a pore size of 3 nm, whereas USCOPs exhibit a surface area of 16 m2 g−1 with a pore size of 19 nm. Therefore, USCOFs formation in aromatic solvents, involving solvation and reduced π–π stacking, which allow the defective intermediates to dissociate and react reversibly, leading to well-ordered molecular arrangements. These solvent characteristics are absent in nonaromatic solvents; therefore, they fail to produce well-ordered molecular arrangement, forming amorphous USCOPs. Finally, the as-synthesized USCOFs were used for a protein(trypsin)-loading and drug delivery application. In addition, the loaded protein retains its original activity. Notably, the conducted MTT assay and cellular uptake proved COF-DOX selectively killed the cancer cells rather than normal cells. TOC: Optimized USCOF reference model along with hydrogen bond and π-π stacking interactions in aromatic solvents results in crystalline USCOFs, which were absent in non-aromatic solvents resulting in amorphous USCOPs. [Display omitted] • Highly crystalline imine linked uniform spherical covalent organic frameworks (USCOFs) and amorphous uniform spherical covalent organic polymers (USCOPs) were constructed using various aromatic and non-aromatic solvents. • The crystalline and non-crystalline nature of the two products were carefully evaluated by the in-situ and ex-situ middle angle scattering. • The high crystalline nature of USCOFs due to the aromatic solvents favoring the thioether hydrogen bonding possibilities between two USCOF units, which was absent in non-aromatic solvents. • The hydrogen bonding between two thioether units of USCOFs was further proved by the density functional theory (DFT) calculations by electron density difference in functional units. • Finally, we applied the USCOFs for protein loading and drug delivery applications. [ABSTRACT FROM AUTHOR]

Particulate methane monooxygenase (pMMO) is known to be the most efficient oxidizer for the conversion of methane (CH4) into methanol (CH3OH) at room temperature. Recently, the tricopper cluster complex [Cu3(7‐N‐Etppz)]1+ has been shown to mediate facile CH4 oxidation upon activation by dioxygen (O2) just like the pMMO enzyme. In this work, we investigate by unrestricted density functional theory (DFT) calculations the oxidation of CH4 on the biomimetic tricopper complex. We find that CH4 can interact with the activated tricopper complex to form a C−H⋅⋅⋅O hydrogen bond between one of the C−H bonds of CH4 and the O2 molecule activating the tricopper cluster complex. We consider both the direct "oxene insertion" mechanism as well as the "hydrogen‐atom abstraction geminal radical rebound" mechanism for the process. Our calculations indicate low kinetic barriers for both reaction pathways, accounting for why the tricopper cluster of the biomimetic complex [Cu3(7‐N‐Etppz)]1+ is a good functional model of the active site in pMMO. [ABSTRACT FROM AUTHOR]

Irgacure 907 (2-Methyl-4′-(methylthio)-2-morpholinopropiophenone) is a highly efficient photoinitiator which undergoes standard Norrish Type I photocleavage. It is widely used to initiate the photopolymerization of chemically unsaturated prepolymers. In this work, the photocleavage reaction mechanisms, as well as excited state properties and the underlying relaxation mechanisms upon photoexcitation of Irgacure 907, are studied using DFT calculations. To investigate the mechanisms, the excited singlet and triplet states have considered in detail. Our calculations indicate that the radical formation for Irgacure 907 originates from the triplet states, which is typical Type-I photoinitiators. Upon irradiation, it will undergo a α-cleavage process to form two radical species. In line with the Jablonski-Type diagram, the ground state of Irgacure 907 excites to a higher state, which is characterized by ππ* singlet state (S 2 ), followed by an internal conversion (IC) to the first excited state (S 1 ). The subsequent intersystem crossing (ISC) can occur between S 1 and triplet state that has nπ* character. As expected, after excitation, the photoinitiator undergoes rapid intersystem crossing (ISC) which is an important step in the photochemical process. [ABSTRACT FROM AUTHOR]

The adsorption configurations of ethane on IrO 2 (110) surface have been investigated using density functional theory (DFT) methods. We find that ethane is most stably adsorbed on IrO 2 (110) surface by interacting with two adjacent Ir cus atoms, which is mainly driven by agostic interaction. We have also performed an elementary step analysis for the ethane dehydrogenation via precursor mediated mechanism on IrO 2 (110) surface. Our results indicate that the activation of ethane on IrO 2 (110) surface is both thermodynamically and kinetically favorable reaction, which is expected to occur at low temperature. Further, we have investigated the role of van der Walls corrections on adsorption and the reaction energetics of ethane dehydrogenation. The results indicate that the contribution of van der Walls corrections has a major impact on ethane adsorption and it facilitates the ethane activation via precursor mediated mechanism instead of desorption. [ABSTRACT FROM AUTHOR]

The adsorption and decomposition mechanism of electrolyte on the cathode surface is one of the governing factors that control the stability, capacity, and cyclic life of Lithium-ion batteries. In this work, first principles calculations are used to study the adsorption and decomposition reaction mechanisms of ethylene carbonate (EC) on the (100) surface of charged (Li 0.6 Mn 2 O 4 ), and the fully discharged LiMn 2 O 4 . The adsorption strength and electronic properties of various configurations are discussed by using density of states (DOS), projected density of states (PDOS) and electron density difference (EDD). Moreover, the initial decomposition mechanisms of EC on the surfaces is investigated by examining the minimum energy path between two minima using the climbing image nudged elastic band reaction-pathway sampling scheme. Even though adsorption and decomposition reaction can occur on the surfaces, for all configurations studied, the results show that the decomposition of EC is more likely on the charged surface despite having higher adsorption energy on the fully discharged surface. In general, this work aims to give an insight into the initial stages of surface catalyzed electrolyte decomposition reactions on spinel cathode structure. [ABSTRACT FROM AUTHOR]

Ethanol adsorption and decomposition on the clean α-Al 2 O 3 (0 0 0 1) surface have been systematically investigated by density functional theory calculations. The nature of the surface-ethanol bonding has studied through the density of states (DOS) and the electron density difference (EDD) contour plots. The DOS patterns confirm that the lone pair electrons of EtOH are involved in the formation of a surface Al O dative bond and the EDD plots provide evidences for the bond weakening/forming, which are consistent with the DOS analysis. Our ethanol decomposition results indicate that ethanol dehydration to ethylene (CH 3 CH 2 OH (a) → C 2 H 4(g) + OH (a) + H (a) ), is the main reaction pathway with the energy barrier of 1.46 eV. Although the cleavage of the hydroxyl group of ethanol has lower energy barrier, the further decomposition of ethoxy owns much higher energy barrier. [ABSTRACT FROM AUTHOR]

• Fe-oxide CNC prepared from Fe(ClO 4) 2 using H 2 O 2(aq) in C 6 H 6 -CH 3 CN. • Fe-oxide CNC composes of Fe 2 O 3 nanoparticles and carbonaceous moiety. • Highly efficient Fe-oxide CNC for highly selective benzene oxidation to phenol. • EPR study shows DMPO-OOH adduct formation on heterogeneous Fe-oxide CNC surface. • Hydrophobic carbonaceous surface assists selective C 6 H 6 oxidation to phenol. Direct benzene hydroxylation under mild conditions using hydrogen peroxide can be essential in producing phenol. A new iron oxide-carbonaceous nanocatalyst (Fe-oxide CNC) is prepared in situ using a precursor of Fe(ClO 4) 2 and H 2 O 2 in benzene and CH 3 CN. The obtained Fe-oxide CNC can efficiently catalyze benzene oxidation to phenol using H 2 O 2(aq) in CH 3 CN. The highest phenol production was achieved with the turnover number (TON) of 122 in unit iron content and selectivity of 96% at 60 °C. The catalyst was characterized by SEM, TEM, XAS, XPS, Raman, XRD, BET, and TGA techniques. Interestingly, materials identification and characterization of the Fe-oxide CNC provided evidence to support the presence of Fe 2 O 3. In addition, the carbonaceous moieties mainly consisted of branched aliphatic hydrocarbons on the iron oxide surface, which enhance the catalytic performance for benzene oxidation to phenol. The Fe-oxide CNC can be recycled three times with comparable catalytic efficiency. Using H 2 18O 2 as an oxidant, the phenol product with highly enriched 18O-atom indicates that the reactive oxygen species (ROS) activated by H 2 O 2(aq) is crucial for aromatic oxidation. Time-resolved spin trapping experiments displayed the formation of the intermediate adducts consisting of 5,5-dimethyl-1-pyrroline N -oxide (DMPO) and reactive oxygenated radicals. For 3‒24 h durations, higher steady-state concentrations of the oxygenated intermediates observed at 25 °C than 60 °C indicate that the catalytic oxidation of benzene mediated by Fe-oxide CNC performs much faster kinetics at 60 °C than the ambient condition. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] Metal free sensitizers were proposed via theoretical methods for DSSC applications. [•] Role of donor/acceptor monomers on absorption spectra were discussed in detail. [•] The absorption bands of designed sensitizers more red shifted than existing dyes. [•] The design strategy of metal free dyes were proposed based on this results. [Copyright &y& Elsevier]

[Display omitted] • IrO 2 /TiO 2 surface is proposed as an efficient low cost catalyst for methane conversion. • Methane dehydrogenation and C-C coupling reactions over IrO 2 /TiO 2 surface are calculated. • The elementary reactions of methane conversion are compared with pure IrO 2 (1 1 0) surface. • IrO 2 /TiO 2 exhibits comparable catalytic activity for methane activation and conversion. Designing an efficient, low-cost catalyst is an important objective in the catalytic conversion of methane into value-added products that would be useful in many technological applications. Although IrO 2 can activate C–H bonds at mild temperature and have excellent catalytic activity towards C–C coupling reactions, the high cost hinders its deployment. Herein, we propose IrO 2 supported on TiO 2 surface (IrO 2 /TiO 2) and investigate its catalytic activity towards the methane dehydrogenation and the possibility of C–C coupling reactions with the help of density functional theory (DFT) calculations. Its catalytic performance is compared with that of a pure IrO 2 surface. We find that the IrO 2 /TiO 2 surface possesses similar adsorption characteristics of CH 4 to the pure IrO 2 surface. Our kinetic results indicate that the proposed catalyst exhibits similar enhanced catalytic activity towards methane activation and its successive dehydrogenation and C-C coupling reactions to that of pure IrO 2 surface. We believe that methane can be more likely activated over the catalyst of one layer IrO 2 supported on TiO 2 at low temperatures, and it shows similar performances in thermodynamics like high-cost pure IrO 2. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of different model dyes on the anatase (101) TiO2 surface has been investigated using density functional theory calculations. The main aim of this study is to investigate the effects of different strength of donor and acceptor groups which are substituted in the present organic dyes on the ability of electron injection to the surface. Analysis of the density of states (DOS) demonstrated that the increased strength of the donor and acceptor dyes shifts the lowest unoccupied molecular orbitals (LUMO) values and decreases the band gap. The strength of the donor and acceptor parts is shown to be effective for the electron injection process. Our present results provide the possibility of the design strategy of dyes to achieve the best dye-sensitized solar cells (DSSCs). [Copyright &y& Elsevier]

Abstract: Two novel conjugated polymers denoted TAZF2 and TAZBTF, having electron-deficient main chains and electron-rich triphenylamine pendant groups, were designed and synthesized. While TAZF2 was constructed with fluorene and electron-deficient 1,2,4-triazole as the major components of the main chain, fluorene, 1,2,4-triazole, and 2,1,3-benzothiadiazole were employed to form TAZBTF. The number-average molecular weights (M w) of the polymers fell in the range of 1.28×104–2.56×104 with polydispersity indexes (PDI= M w/M n) of 1.49–1.95. The polymers had glass transition temperatures (T g) in the range of 153–185°C. While TAZF2 exhibited blue photoluminescence, TAZBTF exhibited yellow–green emission. Thermal stability of the conjugated polymers was enhanced due to the introduction of rigid bipolar components. The incorporation of 2,1,3-benzothiadiazole into TAZBTF reduced the coplanarity of the conjugated polymer, which prohibited the polymer from aggregation. Intramolecular and intermolecular energy transfer was clearly evidenced by the shift in light emission to the yellow–green region. TAZBTF exhibited maximum electroluminescence efficiency as high as 2.60cd/A, demonstrating that a good balance of charge carriers is injected into our devices. [Copyright &y& Elsevier]

Abstract: Deoxygenation of the IrO2(110) surface is investigated at 403–493K, using the core-level spectroscopy and density functional theory (DFT) calculation. The Ir-4f7/2 signals of 1f-cus-Ir with and without on-top oxygen (Otop) emerge as surface features of the baked-out surface, whose positive and negative shifts in binding energy are in line with the DFT computation results. Progressively increasing the reduction temperature, the 1f-cus-Ir feature quickly disappears and the signal of 2f-cus-Ir emerges at 403K. Meanwhile the feature of 1f-cus-Ir+Otop diminishes but persists when the Ir metal signal is evident. The intriguing coexistence of 1f-cus-Ir+Otop and Ir metal at 433–443K is elucidated in the theoretical pathway study. DFT calculation reveals that O2 desorption via pairing two neighboring Otop atoms is the rate-determining step of surface deoxygenation. Under the UHV conditions, Otop is replenished via migration of the surface oxygen species, including the threefold coordinated oxygen (O3f) of a reduced surface. Hence the Otop atom is an active and long-lived surface species, which does not vanish until O3f is consumed and surface Ir begins to cluster. Under the realistic pressure conditions, Otop can also be refreshed via the dissociative adsorption of gas-phase oxygen. In either pathway, Otop is a critical intermediary of IrO2(110) oxidation catalysis. [Copyright &y& Elsevier]

Abstract: Carbon supported RuSe x (x =0.35–2) catalysts of controlled stoichiometry and phase are synthesized via precipitating ruthenium nanoparticles on Vulcan XC-72R, then selenizing ruthenium with hydrogen annealing. The competition for Se between solid-state Ru selenization and volatile selenium hydride formation results in RuSe x nanoparticles with the pyrite structure, the Ru hcp structure, or a mixture of the two. These catalysts are methanol tolerant, and catalytically active toward oxygen reduction reaction (ORR). RuSe x /C (x ≅2) with a pyrite structure, produced at 400°C, exhibits catalytic activity and stability superior to that of RuSe x /C with a ruthenium hcp structure or a mixed phase. And this pyrite RuSe x /C (x ≅2) catalyst yields H2O2 less than 1.5% in the technically pertinent potential range of 0.4–0.6V (vs. Ag/AgCl). Its stability is verified in 100CV cycles, which shows that the catalyst annealed at 400°C is more enduring in potential cycling over 0.65V (vs. Ag/AgCl), compared with the RuSe x /C catalyst annealed at 300°C and the RuSecluster/C reference catalyst prepared by thermolysis of Ru3(CO)12. After CV cycles, the 400°C-annealed catalyst still exhibits a higher ORR activity than the other two catalysts. [Copyright &y& Elsevier]

A series of molecular rotors based on cyclopentane are taken into consideration to explore the influence of different π-donors/acceptors substitution on their efficiency in blue light detection. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods are used to investigate the electronic excitations and photophysical properties of the designed rotors. The influence of mono- and di-substitution on photoisomerization and thermal helix inversion reaction barriers are studied. We find that the di-substitution of a π-donor and a π-acceptor have improved the parent rotor's optical properties towards a longer wavelength. Especially, the rotor R 2,3 (NH 2 , CHO) exhibits the light response range in the blue region (∼408 nm) due to its narrow bandgap (4.94 eV). Our results show that although the substitution of π-donors/acceptors improved the photophysical properties, it has no significant influence on the overall rate-determining thermal helix inversion step barriers. This theoretical work provides new insight into the role of π-donors/acceptors substitution in designing blue light sensors. [Display omitted] • A series of molecular rotors based on cyclopentane was designed for blue light sensing. • Influence of different π-donors/acceptors substitution was explored. • DFT and TDDFT calculations were used to investigate photoisomerization and thermal helix inversion steps. • The rotor with di-substituted π-donor/acceptor R 2,3 (NH 2 , CHO) can be used to detect blue light at ambient conditions. [ABSTRACT FROM AUTHOR]

The status and nature of extraframework Al (EFAl) species in H-mordenite dealuminated by ammonium hexafluorosilicate (i.e., (NH4)2SiF6, AHFS) was investigated. Considerable difference arising from the experimental conditions of AHFS dealumination, that is, in the presence and absence of ammonium acetate (NH4OAc), was observed. Both treatments were not very effective in removing framework aluminum. 27Al and 19F solid-state NMR was used to detect different extraframework aluminum fluoro-complexes resulting from the AHFS dealumination. In the presence of NH4OAc, the essential part of the dealumination process carried on with AHFS was that most of the extracted Al3+ reacted with F- to form (NH4)3AlF6. In the absence of NH4OAc, on the other hand, at least two different forms of aluminum fluoro-complexes other than (NH4)3AlF6 were formed after dealumination. These aluminum fluoro-complexes showed multiple lines located in the range of -144 to -156 ppm in the 19F NMR spectrum. An ab initio method that used both Hartree-Fock and hybrid Hartree-Fock density functional methods at the 6-31+G* basis set level was used to calculate the 19F NMR shifts for discriminating possible aluminum fluoro-complexes. Our results indicated that a combination of NMR and ab initio calculations provided a basis for using them to study EFAl species of unknown compositions and structures. [Copyright &y& Elsevier]