Surface characterization and London dispersive surface free energy of functionalized single-walled carbon nanotubes with a blend of polytetrafluoroethylene by inverse gas chromatography

The SWCNTs and SWCNT-polytetrafluoroethylene (PTFE) blend were prepared by using simple reaction mixture in the presence of chromosorb (SiO₂). Surface morphology of SWCNTs and (SWCNT-PTFE) blend was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and surface BET analysis. In addition, the surface thermodynamic properties of n-alkanes and polar probe net retention volumes are measured by inverse gas chromatography (IGC). The London dispersive surface free energy values were found to be decreased linearly with increase of temperature. The specific component of the surface free energy of adsorption for the polar probes was obtained using the Donnet-Park method. The surface character “S” value (K_b/K_a) at SWCNTs was found to be 0.74, and SWCNT-PTFE blend surface character value was found to be 0.86. This result demonstrates that the (SWCNT-PTFE) blend surface contains relatively more acidic sites then that of SWCNT surface. Therefore, the IGC results provide useful complementary information on the (SWCNT-PTFE) blend surface.     

Revisiting the Structure of Calcined and Hydrated AlPO-11 with DFT-Based Molecular Dynamics Simulations**

Published crystal structures of the AEL-type aluminophosphate AlPO-11 in its calcined form (space group ) show some peculiar features, such as unusually short Al−O and P−O bonds and near-linear Al−O−P angles. Although experimental evidence for the presence of dynamic disorder was presented, the nature of the associated distortions remained unresolved. In this study, ab initio molecular dynamics (AIMD) calculations in the framework of density functional theory (DFT) were employed to study the dynamic behaviour of this zeotype. At 100 K, static local distortions that break the symmetry are present in the time-averaged structures computed from the AIMD trajectories. At 300 and 500 K, the time-averaged structures approach symmetry. Although shortened Al−O and P−O bonds and near-linear Al−O−P angles were found in the average structures, an analysis of radial and angular distribution functions confirmed their absence in the instantaneous structures. This deviation is due to a precession-like motion of some oxygen atoms around the Al−P connection line, which moves their time-averaged positions closer to this line. In hydrated AlPO-11, some of the water molecules are coordinated to framework Al atoms, leading to an octahedral coordination of 1/5 of the Al sites. DFT optimisations and AIMD simulations on partially hydrated models delivered evidence for a preferential adsorption at the Al1 site. No dynamic disorder was observed for the hydrated form.     

The Nature of Hydrogen Adsorption on Platinum in the Aqueous Phase

The thermodynamic state of H₂ adsorbed on Pt in the aqueous phase was determined by kinetic analysis of H₂ reacting with D₂O to HDO, HD, and D₂, and by DFT‐based ab initio molecular dynamics simulations of H₂ adsorption on Pt(111), Pt(110), and Pt nanoparticles. Dissociative adsorption of H₂ on Pt is significantly weakened in the aqueous phase compared to adsorption at gas–solid interfaces. Water destabilizes the adsorbed H atoms, decreasing the heat of adsorption by 19–22 kJ while inducing an additional entropy loss of 50–70 J K^?1. Upon dissociative adsorption of H₂, the average distance of water from the Pt surface increases and the liquid adopts a structure that is more ordered than before close to the Pt surface, which limits the translation mobility of the adsorbed H atoms. The presence of hydrated hydronium ions next to the Pt surface further lowers the H?Pt bond strength.     

DFT characterization of nanostructured germanium surfaces induced by cobalt atoms

By deposition in ultra‐high vacuum of cobalt on a Ge(111)–c(2 × 8) surface, Mocking et al. obtained a surface reconstruction. In the present paper, we analyse the related atomic structure, proposed by these authors, by means of density functional theory calculations. The surface presents ordered clusters that consist of six Ge atoms arranged in a triangle, lying above three Co atoms. The latter are located at substitutional positions within the top plane of the Ge(111) first bilayer. These clusters are similar to what is obtained on part of the Co‐induced Si(111) surface. For this surface, the clusters are terminated either by six Si atoms or by one, two or three adatoms above the six Si atoms. As the Co–Ge clusters systematically display six protrusions in the scanning tunnelling microscopy measurements by Mocking et al., we investigated why Ge adatoms are not present. Comparison of the Gibbs energy, interatomic distances, as well as charge density indicates that Ge adatoms on top of Co‐Ge clusters are less stable than Si adatoms in the Co‐Si system. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of surface properties on the interfacial adhesion in carbon fiber/epoxy composites

A polyacrylonitrile‐based carbon fiber was electrochemically oxidized in an aqueous ammonium bicarbonate solution with current density of up to 2.76 A/m² at room temperature. X‐ray photoelectron spectroscopy revealed that the oxygen content increased with increasing current density before approaching saturation. The increase can be divided into two regions, the rapid increase region (0–1.78 A/m²) and a plateau region (1.78–2.76 A/m²). The surface chemistry analysis showed that the interlaminar shear strength (ILSS) value of the carbon fiber/epoxy composite could be improved by 24.7%. The carbon structure was examined using Raman spectroscopy in terms of order/disorder in the graphite structure and the results indicated that the relative percentage of graphite carbon in the form of sp² hybridization increased above a current density of 1.39 A/m². The increasing non‐polar graphite carbon on the carbon fiber surface decreased the surface energy. As a result, both the surface free energy () and its polar component () decreased when current density increased above 1.78 A/m². The ILSS value had no direct relationship with the nature and surface density of the oxygen‐containing functional groups nor with the carbon structure. It is the surface free energy (), especially the polar component (), which played a critical role in affecting the interfacial adhesion of carbon fiber/epoxy composites. The ILSS value changed with increasing current density and could be divided into three distinct regions, as chemical interaction region (I), anchor force region (II) and matrix damage region (III). Copyright © 2013 John Wiley & Sons, Ltd.     

Anti‐corrosion properties of bis(benzimidazole) derivatives for N80 steel in H2S solution

In this work, we systematically investigated the effect of four bis(benzimidazole) derivatives containing different heteroatoms in molecular structures on inhibiting corrosion of N80 steel in 0.5 mmol·l^?1 H₂S solution by potentiodynamic polarization, electrochemical impedance spectroscopy and metallographic microscope. The results showed that within the range of 0.1–1.0 mmol·l^?1, the adsorption of bis(benzimidazole) derivatives on N80 steel surface was found to follow Langmuir adsorption isotherm. Meanwhile, stable adsorbing monolayer between inhibitors and the metal surface was formed, which was confirmed by thermodynamic adsorption parameters (K_ads, ). This series of bis(benzimidazole) derivatives exhibited obvious corrosion inhibitory properties for N80 steel. Moreover, they could both slow down the anodic dissolution of iron and the cathodic reduction reaction as mixed type corrosion inhibitors. The optimal inhibition efficiency was obtained for 1,3‐bis(benzimidazl‐2‐yl)‐2‐thiapropane (BBMS). Hopefully, this series of inhibitors might find applications in anti‐corrosion and many other areas. Copyright © 2012 John Wiley & Sons, Ltd.     

Adsorption of Acetate on Au(111): An in-situ Scanning Tunnelling Microscopy Study and Implications on Formic Acid Electrooxidation

The adsorption of acetate on an Au(111) electrode surface in contact with acetic acid at pH 2.7 was imaged in-situ using scanning tunnelling microscopy (STM). Two different ordered structures were imaged for acetate adsorbed in the bidentate configuration on the unreconstructed surface at 0.95 V (vs. the saturated calomel electrode, SCE). The first structure, , is metastable and transforms at constant potential within 20 minutes to a structure, which is thermodynamically more favourable. The acetate adlayer starts to form at step edges and propagates via nucleation and growth onto terraces. The findings from in-situ STM are in agreement with the electrochemical behaviour of acetate on Au(111) characterized by voltammetry. A comparison is made with formate adsorption on Au(111). While acetate is not reactive, in contrast to formate, it can act as a spectator species in formic acid electrooxidation.     

Determination of the “Privileged Structure” of 8-Hydroxyquinoline

An accurate semi-experimental equilibrium structure of 8-hydroxyquinoline (8-HQ) has been determined combining experiment and theory. The cm-wave rotational spectrum of 8-HQ was recorded in a pulsed supersonic jet using broadband dual-path reflection and narrowband Fabry-Perot-type resonator Fourier-transform microwave spectrometers. Accurate rotational and quartic centrifugal distortion constants and ¹⁴N quadrupole coupling constants are determined. Rotational constants of all ¹³C, ¹⁸O and ¹⁵N singly substituted isotopologues in natural abundance and those of a chemically synthesized OD isotopologue were used to obtain geometric parameters for all the heavy atoms and the hydroxyl hydrogen from a number of structure determination models. Theoretical approaches allowed for the determination of a semi-experimental equilibrium structure, in which computed rovibrational and electronic corrections were utilized to convert vibrational ground state constants into equilibrium constants. Despite the molecule having only a horizontal plane of symmetry and possessing 11 individual heavy atoms, microwave spectroscopy has allowed for a reliable and accurate structure determination. A mass dependent, structure was determined and proved to be equally reliable by comparison with the B3LYP-D3(BJ)/aVTZ equilibrium structure.     

Tuning the Hybridization of Local Exciton and Charge-Transfer States in Highly Efficient Organic Photovoltaic Cells

Decreasing the energy loss is one of the most feasible ways to improve the efficiencies of organic photovoltaic (OPV) cells. Recent studies have suggested that non-radiative energy loss ( ) is the dominant factor that hinders further improvements in state-of-the-art OPV cells. However, there is no rational molecular design strategy for OPV materials with suppressed . Herein, taking molecular surface electrostatic potential (ESP) as a quantitative parameter, we establish a general relationship between chemical structure and intermolecular interactions. The results reveal that increasing the ESP difference between donor and acceptor will enhance the intermolecular interaction. In the OPV cells, the enhanced intermolecular interaction will increase the charge-transfer (CT) state ratio in its hybridization with the local exciton state to facilitate charge generation, but simultaneously result in a larger . These results suggest that finely tuning the ESP of OPV materials is a feasible method to further improve the efficiencies of OPV cells.     

Linear Adsorption Enables NO Selective Electroreduction to Hydroxylamine on Single Co Sites

Hydroxylamine (NH₂OH), a vital industrial feedstock, is presently synthesized under harsh conditions with serious environmental and energy concerns. Electrocatalytic nitric oxide (NO) reduction is attractive for the production of hydroxylamine under ambient conditions. However, hydroxylamine selectivity is limited by the competitive reaction of ammonia production. Herein, we regulate the adsorption configuration of NO by adjusting the atomic structure of catalysts to control the product selectivity. Co single-atom catalysts show state-of-the-art NH₂OH selectivity from NO electroreduction under neutral conditions (FE : 81.3 %), while Co nanoparticles are inclined to generate ammonia (FE : 92.3 %). A series of in situ characterizations and theoretical simulations unveil that linear adsorption of NO on isolated Co sites enables hydroxylamine formation and bridge adsorption of NO on adjacent Co sites induces the production of ammonia.     

Highly Selective Electrochemical Reduction of CO2 to Alcohols on an FeP Nanoarray

Electrochemical reduction of CO₂ into various chemicals and fuels provides an attractive pathway for environmental and energy sustainability. It is now shown that a FeP nanoarray on Ti mesh (FeP NA/TM) acts as an efficient 3D catalyst electrode for the CO₂ reduction reaction to convert CO₂ into alcohols with high selectivity. In 0.5 m KHCO₃, such FeP NA/TM is capable of achieving a high Faradaic efficiency (FE ) up to 80.2 %, with a total FE of 94.3 % at ?0.20 V vs. reversible hydrogen electrode. Density functional theory calculations reveal that the FeP(211) surface significantly promotes the adsorption and reduction of CO₂ toward CH₃OH owing to the synergistic effect of two adjacent Fe atoms, and the potential‐determining step is the hydrogenation process of *CO.     

Core level photoemission line shape selection: Atomic adsorbates on iron

Robust fitting of core level photoemission spectra is often central to reliable interpretation of X-ray photoelectron spectroscopy (XPS) data. One key element is employment of the correct line shape function for each spectral component. In this study, we consider this topic, focusing on XPS data from atomic adsorbates, namely, O and S, on Fe(110). The potential of employing density functional theory (DFT) for generating adsorbate projected electronic density of states (PDOS) to support line shape selection is explored. O 1s core level XPS spectra, acquired from various ordered overlayers of chemisorbed O, all display an equivalent asymmetric line shape. Previous work suggests that this asymmetry is a result of finite O PDOS in the vicinity of the Fermi level, allowing O 1s photoexcitation to induce a weighted continuum of final states through electron-hole pair excitation. This origin is corroborated by O DFT-PDOS generated for an optimised five-layer Fe(110)(2 × 2)-O slab. Adsorbate DFT-PDOS were also computed for Fe(110) -S. As, similar to adsorbed O, there is a significant continuous distribution of states about the Fermi level, it is proposed that the S 2p XPS core levels should also have asymmetric profiles. S 2p XPS data acquired from Fe(110) -S, and their subsequent fitting, verify this prediction, suggesting that DFT-PDOS could aid line shape selection.     

Tuning the Hybridization of Local Exciton and Charge‐Transfer States in Highly Efficient Organic Photovoltaic Cells

Decreasing the energy loss is one of the most feasible ways to improve the efficiencies of organic photovoltaic (OPV) cells. Recent studies have suggested that non‐radiative energy loss ( ) is the dominant factor that hinders further improvements in state‐of‐the‐art OPV cells. However, there is no rational molecular design strategy for OPV materials with suppressed . Herein, taking molecular surface electrostatic potential (ESP) as a quantitative parameter, we establish a general relationship between chemical structure and intermolecular interactions. The results reveal that increasing the ESP difference between donor and acceptor will enhance the intermolecular interaction. In the OPV cells, the enhanced intermolecular interaction will increase the charge‐transfer (CT) state ratio in its hybridization with the local exciton state to facilitate charge generation, but simultaneously result in a larger . These results suggest that finely tuning the ESP of OPV materials is a feasible method to further improve the efficiencies of OPV cells.     

In situ friction study of Ag Underpotential deposition (UPD) on Au(111) in aqueous electrolyte

The electrodeposition of silver on Au(111) was investigated using lateral force microscopy (LFM) in Ag⁺ containing sulfuric acid. Friction force images show that adsorbed sulfate forms structure ( on Au(111) prior to Ag underpotential deposition (UPD) and structure ( ) on a complete monolayer or bilayer of Ag. Variation of friction with normal load shows a non-monotonous dependence, which is caused by increasing penetration of the tip into the sulfate adlayer. In addition, the friction force is influenced by the varying coverage and mobility of Ag atoms on the surface. Before Ag coverage reaches the critical value, the deposited silver atoms may be mobile enough to be dragged by the movement of AFM tip. Possible penetration of the tip into the UPD layer at very high loads is discussed as a model for self-healing wear. However, when the coverage of Ag is close to 1, the deposited Ag atoms are tight enough to resist the influence of the AFM tip and the tip penetrates only into the sulfate adlayer.     

Surface thermodynamics of Efavirenz and a blend of Efavirenz with cellulose acetate propionate by inverse gas chromatography

The purpose of this paper is to study the effect of an excipient on the surface energetics of Efavirenz (EFV) drug. The net retention volumes, V_N, for n‐alkanes and polar solutes on the two columns, namely, EFV drug and a blend of EFV with cellulose acetate propionate have been measured by inverse gas chromatography. The dispersive surface free energy, , Lewis acid parameter, K_a, and Lewis base parameter, K_b, have been determined using V_N values. The values are decreased linearly with increase of temperature for pure EFV as well as for the blend. Furthermore, the values of EFV are higher than in the blend, for example, values at T = 318.15 K for EFV, and for the blend are 28.09 ± 6.02 mJ/m² and 28.30 ± 2.31 mJ/m², respectively. The specific component of surface free energy has been obtained by the Schultz method as well as by the Dong et al. method. The values have been used to calculate Lewis acid‐base parameters for the EFV as well as the blend. The K_a values for the EFV and the blend are almost similar, where as the K_b values are higher in EFV than in the blend. Similar trend in K_a and K_b has been observed in both methods studied. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of Urbach Energy,Temperature, and Longitudinal Position in the Active Layer on Carrier Diffusion Length in Perovskite Solar Cells

The diffusion length of charge carriers in the active layer of a perovskite solar cell (PSC) of the structure Glass/PEDOT: PSS/CH₃NH₃PbI₃/PC60BM/Al is modelled. It is found that the diffusion length depends on the position x in the active layer measured from the PEDOT: PSS interface, Urbach energy and temperature. By varying the voltage in the range from zero to , it is shown that the dependence of diffusion length on the position x in the active layer reduces at higher voltage. The combined influence of applied voltage and temperature on the diffusion length of charge carriers is investigated and it is found that in the low voltage range the diffusion length is temperature independent, but it becomes significantly temperature dependent at higher voltages. Also, it is found that the diffusion length decreases as the applied voltage increases and this reduction becomes much more significant at higher voltage and temperatures. The combined influence of applied voltage and Urbach energy on diffusion length of charge carriers reveals that the diffusion length decreases when both the applied voltage and Urbach energy increase. However, the reduction in the diffusion length due to the increase in Urbach energy becomes less significant at higher voltage.     

Copper 1,19‐Diaza‐21,24‐dicarbacorrole: A Corrole Analogue with an N−N Linkage Stabilizes a Ground‐State Singlet Organocopper Species

A copper complex of a heterocorrole analogue with an N–N linkage, 1,19‐diaza‐21,24‐dicarbadibenzocorrole ( Cu‐5 ), was successfully synthesized via oxidative metalation–cyclization of a tetrapyrrolic precursor. The N–N linkage in the skeleton of Cu‐5 , which serves as a mediator of π‐electron delocalization, features an 18π aromatic system. The electronic structure of Cu‐5 is best described as a ground‐state singlet species stabilized by the distinct NNCC coordination core. This finding shows how the ligand's design can be used to modulate the Cu orbital energy, thereby making such compounds invaluable for copper‐based catalytic applications.     

Copper 1,19-Diaza-21,24-dicarbacorrole: A Corrole Analogue with an N−N Linkage Stabilizes a Ground-State Singlet Organocopper Species

A copper complex of a heterocorrole analogue with an N–N linkage, 1,19-diaza-21,24-dicarbadibenzocorrole ( Cu-5 ), was successfully synthesized via oxidative metalation–cyclization of a tetrapyrrolic precursor. The N–N linkage in the skeleton of Cu-5 , which serves as a mediator of π-electron delocalization, features an 18π aromatic system. The electronic structure of Cu-5 is best described as a ground-state singlet species stabilized by the distinct NNCC coordination core. This finding shows how the ligand's design can be used to modulate the Cu orbital energy, thereby making such compounds invaluable for copper-based catalytic applications.     

First-principles study of the magnetic exchange forces between the RuO2(110) surface and Fe tip

Magnetic exchange force microscopy (MExFM) is an important experimental technique for mapping the magnetic structure of surfaces with atomic resolution relying on the spin-dependent short-range exchange interaction between a magnetic tip and a magnetic surface. RuO₂ is a significant compound with applications in heterogeneous catalysis and electrocatalysis. It has been characterized recently as an antiferromagnetic (AFM) material, and its magnetism has been predicted somewhat surprisingly to play an important role in its catalytic properties. In the current study, we explore theoretically whether MExFM can visualize the magnetic surface structure of RuO₂. We use density functional theory (DFT) calculations to extract the exchange interactions between a ferromagnetic Fe tip interacting with an AFM RuO₂(110) surface, as a function of tip-surface distance and the position of the tip over the surface. Mimicking the MExFM experiment, these data are then used to calculate the normalized frequency shift of an oscillating cantilever tip versus the minimum tip-surface distance, and construct corrugation height line profiles. It is found that the exchange interaction between tip and surface is strongest for a parallel configuration of the spins of the tip and of the surface; it is weakest for an anti-parallel orientation. In a corrugation profile, this gives rise to a sizable height difference of 25 pm between the spin-up and spin-down Ru atoms in the RuO₂(110) surface at a normalized frequency shift =−10.12 fNm^1/2. The O atoms in the surface are not or hardly visible in the corrugation profile.     

Comparison of the periodic slab approach with the finite cluster description of metal–organic interfaces at the example of PTCDA on Ag(110)

We present a comparative study of metal–organic interface properties obtained from dispersion corrected density functional theory calculations based on two different approaches: the periodic slab‐supercell technique and cluster models with 32–290 Ag atoms. Fermi smearing and fixing of cluster borders are required to make the cluster calculation feasible and realistic. The considered adsorption structure and energy of a PTCDA molecule on the Ag(110) surface is not well reproduced with clusters containing only two metallic layers. However, all clusters with four layers of silver atoms and sufficient lateral extension reproduce the adsorbate structure within 0.04 Å with respect to the slab‐supercell structure and provide adsorption energies of ( 0.08 eV) consistent with the slab result of −4.47 eV. Thus, metal–organic adsorbate systems can be realistically represented by properly defined cluster models. © 2018 Wiley Periodicals, Inc.