Combination Of X-ray Photoelectron Spectroscopy Research Articles

Effect of surface modification on wettability and tribology by laser texturing in Al2O3.

The life of ceramic tools restricts the development of the manufacturing industry and can be increased through the enhancement of surface performance. Laser surface texturing is a feasible technology to improve ceramic tool life based on the relationship between surface properties and the laser-texturing process. In this study, ${{\rm Al}_2}{{\rm O}_3}$ substrates have been textured by an ytterbium fiber laser system with a wavelength of 1064 nm and a pulse duration of 50 ns. First, the damage threshold of ${{\rm Al}_2}{{\rm O}_3}$ was measured to provide a basis for selecting laser-texturing parameters. The surface morphology was characterized using a white confocal scanning microscope and a scanning electron microscope to investigate the characteristics of laser processing. Water contact angles were measured to investigate the relationship between laser parameters and changes in wettability. The surface energy of the superhydrophobic ceramic was calculated based on the contact angle. Combined X-ray photoelectron spectroscopy (XPS) measurement was used to explore the mechanism of wettability changes from the chemical component and microstructure perspectives. The friction coefficient of ${{\rm Al}_2}{{\rm O}_3}$ was determined by a ball-on-disc wear test. The results showed that laser texturing can significantly improve the surface hydrophobicity and friction stability.

Iodine local environment in high pressure borosilicate glasses: An X-ray photoelectron spectroscopy and X-ray absorption spectroscopy investigation

• Iodine is dissolved as iodide (I − ) in high pressure borosilicate glasses. • Both alkali and alkaline-earth cations act as a charge compensator to I − species. • The absence of iodate (I 5+ ) suggests that there is a complex interplay between I − species and oxygen species within the glass structure. The 129 I radioactive isotope is a by-product of nuclear plants activity. Owing to its strong volatility, there is currently no ideal protocol to immobilize 129 I in nuclear waste borosilicate glasses. Recently, we have proposed the use of high-pressure syntheses to dissolve iodine in various glass compositions; however, I speciation and dissolution mechanism could not be determined. We have adopted an approach combining X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) methods to determine I speciation and molecular environment in glasses containing from 0.5 to 2.5 mol.% I. The XPS spectra reveal that I is mostly dissolved as iodide (>85% I − ) with a small proportion of elemental iodine (<15% I 0 ) and the absence of iodate species (I 5+ ). For borosilicate glasses, the XAS results and subsequent spectrum simulations suggested that Na and Ca are involved in the I − vicinity with averaged derived coordination number (CN) of 3.6 and 2.0 and bond length to the nearest neighbour (r X-I ) 2.98 and 2.85 Å, respectively. These results suggest that the coexistence of both I − and I 5+ species is not requested for electric neutrality but instead, we explain the I speciation by the possible interplay with oxygen species from the borosilicate matrix. In addition, the results imply that the borosilicate network is affected by the I dissolution.

Insight into degradation mechanism of Pd nanoparticles on NCNTs catalyst for ethanol electrooxidation: A combined identical-location transmission electron microscopy and X-ray photoelectron spectroscopy study

Herein, we report a facile method to prepare palladium nanoparticles (Pd NPs) anchored on nitrogen-doped carbon nanotubes (Pd/NCNTs) with particle size distribution uniformed. The Pd/NCNTs exhibits excellent ethanol oxidation reaction (EOR) mass activity of 2,489 A g−1, which is 5.1 times higher than commercial Pd/C. However, the anodic reaction of EOR suffers from poor efficiency and low durability. In order to solve the problem of low durability and have better understanding of the degradation mechanism of anodic catalysts, identical-location transmission electron microscopy (IL-TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were carried out. These were applied to Pd/NCNTs catalyst under EOR in alkaline media. The results showed that the leaching of Pd NPs and the reduction of surface metallic Pd0 were the main reasons for the decreased EOR activity. These findings provide practical guidance for the development of catalysts with higher activity and stability for energy conversion.

Area-selective Electron-beam induced deposition of Amorphous-BNx on graphene

Thin, stable and inert dielectric spacers are essential for manufacturing electronic devices based on 2D materials. However, direct synthesis on top of 2D materials is difficult due to their inert nature. In this work, we studied how an electron beam induces fragmentation of borazine and enables spatially confined synthesis of amorphous-BNx on graphene at room temperature. Using a combination of X-ray Photoelectron Spectroscopy, Low Energy Electron Microscopy, and Scanning Tunneling Microscopy we studied the morphology of the heterostructure, its chemical composition, and finally its temperature evolution. We find that electron-beam induced deposition starts by the binding of heavily fragmentized borazine, including atomic boron, followed by the growth of a multilayer with a 1:0.7 B:N ratio. The final structure exhibits a thermal stability up to 1400 K and ~ 50 nm spatial control provided by the electron beam. Our studies provide surface science insight into the use of electron beams for synthesis and lateral control of stable and inert layers in 2D heterostructures.

Purification of polyynes via carbides

The synthesis of carbyne has remained an elusive goal for decades. One of the significant reasons is that high-purity and high-concentration hydrogen end-capped polyynes (C2nH2) as the most important model molecule and precursors for carbyne have been not widely prepared. Herein, we develop a facile and universal strategy to obtain high-purity and high-concentration C8-18H2 molecules using solid linear carbon chains with silver atom ending-capped (Ag2C8-18) as reaction precursors. The purified and concentrated C8-18H2 solution and Ag2C8-18 powder are evaluated by a combination of X-ray photoelectron spectroscopy, nuclear magnetic resonance spectroscopy, Raman spectroscopy, UV–vis–NIR spectroscopy and transmission electron microscope. These results confirm that the high-purity and high-concentration C2nH2 are obtained through the reaction of metal carbides solid and hydrogen chloride molecule. Our strategy for investigating unprotected linear carbon chains in solid and the successful preparation of high-concentration C2nH2 from solid carbides provide a new avenue for the research of linear carbon chains.

Thermal Transformation of Sulfur Species and Hydrogen Sulfide Formation in High-Pyrite-Containing Lacustrine Type-II Shale during Semiopen Pyrolysis

The shale of the seventh member of the Triassic Yanchang Formation in the Ordos Basin (abbreviated as Chang 7 shale) is the most prospective shale for in situ conversion process. In our previous study, a series of artificial maturation experiments were conducted to simulate the hydrocarbon generation–retention–expulsion process. However, during the experiments, a large amount of hydrogen sulfide (H₂S) was generated along with hydrocarbon products. Therefore, in this study, a combination of X-ray photoelectron spectroscopy, X-ray diffraction, and elemental analysis was used to reveal the thermal transformation of sulfur species and the formation process of H₂S. The results showed that kerogen decomposition and the corresponding products exert a strong influence on the transformation of organic sulfur and pyritic sulfur and, thus, on H₂S formation. Before the peak hydrocarbon-generating stage (<0.6% Rₒ, 340 °C), the H₂S yield was very low, primarily originating from organic sulfur in the kerogen. During the peak hydrocarbon generation and secondary cracking stage (0.6–1.24% Rₒ, 340–400 °C), the H₂S content showed an noticeable increase, and because the bulk atomic Sₒᵣg/C ratio remained relatively constant, the main source of H₂S changed from organic sulfur to inorganic sulfur. Kerogen decomposition, pyrite decomposition, and thermochemical sulfate reduction (TSR) reactions contributed to H₂S formation, whereas secondary pyrite formation consumed H₂S. When the hydrocarbon generation potential of kerogen was almost exhausted, H₂S exhibited an abnormally sharp increase, and little or no secondary pyrite was formed. The sulfur generated by pyrite decomposition partly formed H₂S and partly incorporated into the organic matrix of kerogen. Hydrogen radicals generated by kerogen decomposition and secondary oil cracking are proposed as the controlling factor in the initial pyrite decomposition of the Chang 7 shale under the present pyrolysis experimental conditions.

Boosting polysulfide redox conversion of Li-S batteries by one-step-synthesized Co-Mo bimetallic nitride

Lithium-sulfur (Li-S) batteries are considered as one of the most promising next generation energy storage systems due to the high theoretical specific capacity, low cost, and environmental benignity. However, the notorious shuttle effect of polysulfides hinders the practical application of Li-S batteries. Herein, we have rationally designed and synthesized sea urchin-like Co-Mo bimetallic nitride (Co3Mo3N) in the absence of additional nitrogen sources with only one step, which was applied as the sulfur host materials for Li-S batteries. The results indicate that Co3Mo3N can efficiently anchor and catalyze the conversion of polysulfides, thus accelerating the electrochemical reaction kinetics and enabling prominent electrochemical properties. As a consequence, the S@Co3Mo3N cathode exhibits a high rate performance of 705 mAh g−1 at 3 C rate and an excellent cycling stability with a low capacity fading rate of 0.08% per cycle at 1 C over 600 cycles. Even at a high sulfur loading of 5.4 cmg cm−2, it delivers a high initial areal capacity of 4.50 mAh cm−2, which is still retained at 3.64 mAh cm−2 after 120 cycles. Furthermore, the catalytic mechanism and structural stability of Co3Mo3N during cycling were elucidated by a combination of X-ray photoelectron spectroscopy and X-ray absorption fine structure. This work highlights the strategy of structure-catalysis engineering of bimetallic nitride, which is expected to have a wide application in Li-S batteries.

Carbon doping-induced defect centers in anodized alumina with enhanced optically stimulated luminescence

Anodized aluminum oxide (AAO) in amorphous form is shown to be a prospective phosphor for optically stimulated luminescence (OSL) by implanting 50 keV carbon ions at a fluence of 1 × 1016 ions/cm2 at room temperature. An almost 20-fold enhancement in continuous wave OSL (CW-OSL) sensitivity is obtained in carbon-doped AAO (C:AAO) by exposing to beta radiation, while an almost linear increase in CW-OSL intensity is recorded with increasing dose from 0.3 to 5 Gy. However, cathodoluminescence (CL) suggests an upsurge of oxygen vacancies, especially F+ and F22+ centers, at the cost of F center-related defects in C:AAO. Detailed X-ray photoelectron spectroscopy (XPS) analysis further reveals that the implanted carbon atoms can act as cationic impurities in AAO and stabilize the nearby F+ centers via substitution of Al3+ by C2+. The combined CL and XPS results are also shown to be capable of illustrating the CW-OSL response. This study would, therefore, be a benchmark for understanding the role of carbon in the substitutional sites of AAO for generating OSL active electron traps.

An XPS and ToF-SIMS study of the passive film formed on a model FeCrNiMo stainless steel surface in aqueous media after thermal pre-oxidation at ultra-low oxygen pressure

A combined X-ray photoelectron spectroscopy, time-of-fight secondary ion mass spectrometry and electrochemical approach was used to investigate the mechanisms of molybdenum and chromium enrichment of a passive film formed on a model austenitic stainless steel single crystal in aqueous acid media and the effect that thermal pre-oxidation at 250°C plays in the composition, thickness and stratification of the film. A clean FeCrNiMo (1 0 0)-oriented surface, prepared under ultra-high vacuum (UHV), was exposed to ultra-low pressures of oxygen at 250°C, forming a thin oxide film, rich in iron and chromium, as well as containing molybdenum. An argon-filled glovebox, directly attached to the UHV system, allowed for electrochemical alterations to be carried out without exposure to ambient air. After being held at open circuit potential for 30 min, hydroxylation of chromium and molybdenum was promoted, with a marked enrichment of both elements in the oxide film. A distinct bilayer film was observed. Anodic polarisation resulted in a significant growth of the inner layer and further enrichment of chromium. Pre-oxidation at 250°C, using an ultra-low pressure of oxygen, was found to promote protection against transient active dissolution during anodic passivation, and to cause enrichment of molybdenum in the outer layer of the passive film.

New Insights into the N-S Bond Formation of a Sulfurized-Polyacrylonitrile Cathode Material for Lithium-Sulfur Batteries.

Sulfurized polyacrylonitrile (S-cPAN) has been recognized as a particularly promising cathode material for lithium-sulfur (Li-S) batteries due to its ultra-stable cycling performance and high degree of sulfur utilization. Though the synthetic conditions and routes for modification of S-cPAN have been extensively studied, details of the molecular structure of S-cPAN remain yet unclear. Herein, a more reasonable molecular structure consisting of pyridinic/pyrrolic nitrogen (NPD/NPL) is proposed, based on the analysis of combined X-ray photoelectron spectroscopy, 13C/15N solid-state nuclear magnetic resonance, and density functional theory data. The coexistence of vicinal NPD/NPL entities plays a vital role in attracting S2 molecules and facilitating N-S bond formation apart from the generally accepted C-S bond in S-cPAN, which could explain the extraordinary electrochemical features of S-cPAN among various nitrogen-containing sulfurized polymers. This study provides new insights and a better understanding of structural details and relevant bond formation mechanisms in S-cPAN, providing a foundation for the design of new types of sulfurized cathode materials suitable for application in next-generation high-performance Li-S batteries.

Hf1−xZrxO2 and HfO2/ZrO2 gate dielectrics with extremely low density of interfacial defects using low temperature atomic layer deposition on GaN and InP

Achieving a negative capacitance field effect transistor with a subthreshold swing beyond the Boltzmann limit requires a “defect-free” dielectric-semiconductor interface. We grew alloyed (Hf1−xZrxO2) and stacked (HfO2/ZrO2) gate dielectrics on GaN and InP substrates using low temperature plasma enhanced atomic layer deposition. In situ ellipsometry data show that alloying hafnia with zirconia reduces the refractive index and widens the bandgap. The stacked and alloyed structures reveal very low capacitance-voltage hysteresis of 35 and 45 mV, respectively, on GaN. The density of interfacial traps as low as 1.12 × 1010 cm−2 eV−1 was achieved on GaN mainly due to the combination of very low dielectric growth temperature (100 °C) and high postfabrication heat treatment temperature (510 °C). The conduction and valence band offsets of the alloyed gate dielectrics on InP were measured and compared to pure zirconia using a combination of x-ray photoelectron spectroscopy and ellipsometry. The alloyed structures show a wider bandgap, larger conduction band offset, and smaller valence band offset compared to pure zirconia. This was attributed to the increase in the valence band width with hafnia addition, which reduces the alloyed gate dielectric’s valence band offset. We resolved the band structure alignement to be type I with band offsets of 3.53 eV for electrons and 1.03 eV for holes in Hf0.25Zr0.75O2/InP heterojunctions. The results allow for a clear and detailed picture of two distinct growth procedure that affect the interfacial defect concentration.

Oxidation of aluminum thin films protected by ultrathin MgF2 layers measured using spectroscopic ellipsometry and X-ray photoelectron spectroscopy

To maintain high, broad-band reflectance, thin transparent fluoride layers, such as MgF2, are used to protect aluminum mirrors against oxidation. In this study, we present, for the first time, combined X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometric (SE) studies of aluminum oxidation as a function of MgF2 overlayer thickness (thickness 0-5 nm). Dynamic SE tracks the extent of oxide growth every ca. 2s over a period of several hours after the evaporated Al + MgF2 bilayer is removed from the deposition chamber. Aluminum oxidation changes under the fluoride layer were quantitatively verified with XPS. Changes in chemical state from Al metal to Al oxide were directly observed. Oxide growth is computed from relative XPS peak areas as corrected for electron attenuation through the MgF2 overlayer. An empirical formula fits time-dependent data for aluminum surfaces protected by MgF2 as a function of MgF2 layer thickness: aluminum-oxide thickness = kSE*log(t)+bSE. The slope depends only on MgF2 thickness, decreasing monotonically with increasing MgF2 thickness. This method of employing SE coupled with XPS can be extendable to the study of other metal/overlayer combinations.

The influence of the amino group in 3-amino-1,2,4-triazole corrosion inhibitor on the interface properties for brass studied by ToF-SIMS.

RationaleThe detailed surface analysis of corrosion inhibitor surface layers by the application of 1,2,4‐triazole (TRI) and 3‐amino‐1,2,4‐triazole (3‐AT) compounds adsorbed from a 3 wt. % NaCl solution on the brass surface was performed by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The results obtained were additionally supported by X‐ray photoelectron spectroscopy (XPS) measurements.MethodsThe description of the corrosion inhibitor surface layers was elaborated by using ToF‐SIMS and molecular‐specific signals. Characteristic molecular‐specific signals were used to perform 2D ToF‐SIMS imaging and cooling/heating experiment associated with ToF‐SIMS measurements. A detailed surface analysis using high‐resolution angle‐resolved XPS and gas cluster ion beam sputtering in combination with XPS measurements was also carried out.ResultsOrganometallic complexes were formed after the corrosion process of brass with the release of Cu and Zn ions that subsequently connect with TRI or 3‐AT. Using ToF‐SIMS, possible spectral interferences of the organometallic species were considered due to the presence of different organometallic compounds composed of the two main Cu and Zn isotopes, that is, 63Cu and 65Cu and 64Zn and 66Zn. Using the molecular‐specific signals, 2D imaging was performed, which showed a different distribution of different species on the brass surface. In addition, a ToF‐SIMS experiment on thermal stability showed that most of the TRI‐ and 3‐AT‐related species desorb from the brass surface at 460 °C and 405 °C, respectively.ConclusionsToF‐SIMS analysis confirmed the formation of Cu/Zn‐ or Cu2‐inhibitor organometallic complexes, whereas the formation of Zn2‐inhibitor organometallic complexes on the brass surface was not confirmed. ToF‐SIMS imaging showed complete coverage of the brass surface with different Cu/Zn‐ or Cu2‐inhibitor organometallic complexes. The high thermal stability of the corrosion inhibitor surface layers was confirmed by ToF‐SIMS.

Topology Selectivity in On-Surface Dehydrogenative Coupling Reaction: Dendritic Structure versus Porous Graphene Nanoribbon.

Selective control on the topology of low-dimensional covalent organic nanostructures in on-surface synthesis has been challenging. Herein, with combined scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we report a successful topology-selective coupling reaction on the Cu(111) surface by tuning the thermal annealing procedure. The precursor employed is 1,3,5-tris(2-bromophenyl)benzene (TBPB), for which Ullmann coupling is impeded due to the intermolecular steric hindrance. Instead, its chemisorption on the Cu(111) substrate has triggered the ortho C-H bond activation and the following dehydrogenative coupling at room temperature (RT). In the slow annealing experimental procedure, the monomers have been preorganized by their self-assembly at RT, which enhances the formation of dendritic structures upon further annealing. However, the chaotic chirality of dimeric products (obtained at RT) and hindrance from dense molecular island make the fabrication of high-quality porous two-dimensional nanostructures difficult. In sharp contrast, direct deposition of TBPB molecules on a hot surface led to the formation of ordered porous graphene nanoribbons and nanoflakes, which is confirmed to be the energetically favorable reaction pathway through density functional theory-based thermodynamic calculations and control experiments. This work demonstrates that different thermal treatments could have a significant influence on the topology of covalent products in on-surface synthesis and presents an example of the negative effect of molecular self-assembly to the ordered covalent nanostructures.

Creating Ferromagnetic Insulating La0.9Ba0.1MnO3 Thin Films by Tuning Lateral Coherence Length.

In this work, heteroepitaxial vertically aligned nanocomposite (VAN) La0.9Ba0.1MnO3 (LBMO)-CeO2 films are engineered to produce ferromagnetic insulating (FMI) films. From combined X-ray photoelectron spectroscopy, X-ray diffraction, and electron microscopy, the elimination of the insulator–metal (I–M) transition is shown to result from the creation of very small lateral coherence lengths (with the corresponding lateral size ∼ 3 nm (∼7 u.c.)) in the LBMO matrix, achieved by engineering a high density of CeO2 nanocolumns in the matrix. The small lateral coherence length leads to a shift in the valence band maximum and reduction of the double exchange (DE) coupling. There is no “dead layer” effect at the smallest achieved lateral coherence length of ∼3 nm. The FMI behavior obtained by lateral dimensional tuning is independent of substrate interactions, thus intrinsic to the film itself and hence not related to film thickness. The unique properties of VAN films give the possibility for multilayer spintronic devices that can be made without interface degradation effects between the layers.

Adsorptive-photocatalytic performance and mechanism of Me (Mn,Fe)-N co-doped TiO2/SiO2 in cyanide wastewater

In this study, Me (Mn, Fe)-N co-doping is used to improve the treatment efficiency of TiO2/SiO2 on cyanide wastewater, and to explore the reasons for the change in the catalytic performance of the material. The characteristics of the materials are studied by field emission scanning electron microscopy (FESEM)/ energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Brunner−Emmet−Teller (BET), Thermal gravimetric analyzer (TGA) and UV–vis spectrometer, which indicate that TiO2 is anatase type with a particle size of 10–11 nm; Doping elements (Fe, N, and Mn) are well dispersed in the material; Fe or Mn doping can increase the specific surface area of TiO2, while N doping has the opposite effect. Further, the comparison of the treatment effects of cyanide wastewater by TiO2/SiO2 doped with single (N, Fe, Mn) and co-doped with Me (Mn, Fe)-N demonstrates that the materials co-doped with Mn-N possesses the most efficient photocatalytic performance. The degradation efficiency of cyanide reaches 97.09% and the adsorption removal efficiencies of copper and zinc ions reach 88.54% and 100% under light irradiation within 2 h. The mechanism of Mn-N co-doped synergistic catalysis has been studied by combining X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). This indicates that the reason for the significant improvement of the photocatalytic performance of the material is that co-doping produced a new electronic states that overlaps the valence band of TiO2, which promotes the transfer of photogenerated carriers and reduces the electron-hole recombination. This work can efficiently and cleanly decompose cyanide while adsorbing and removing heavy metals, which may be of great significance to the development of the gold industry.

Highly efficient oxygen evolution and stable water splitting by coupling NiFe LDH with metal phosphides

It is a great challenge to develop highly active oxygen evolution reaction (OER) electrocatalysts with superior durability. In this study, a NiFe layered double hydroxide-decorated phosphide (NiFe LDH@CoP/NiP3) was constructed to display satisfactory OER activity and good stability for water splitting in alkaline media. At an overpotential of 300 mV, NiFe LDH@CoP/NiP3 achieved a current density of 82 mA cm−2 for the OER, which was 9.1 and 2.3 times that of CoP/NiP3 and NiFe LDH, respectively. Moreover, the reconstruction behavior, during which oxyhydroxides formed, was studied by a combination of X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning electron microscopy. A synergistic effect between NiFe LDH and CoP/NiP3 was also observed for the hydrogen evolution reaction. Furthermore, when NiFe LDH@CoP/NiP3 acted as both the cathode and anode for overall water splitting, a high current density of 100 mA cm−2 was maintained for more than 275 h. In addition, under Xe light irradiation, a solar to hydrogen efficiency of 9.89% was achieved for solar-driven water splitting. This work presents the coupling of different active compositions, and can provide a reference for designing bifunctional electrocatalysts.

Experimental measurement and prediction of ionic liquid ionisation energies.

Ionic liquid (IL) valence electronic structure provides key descriptors for understanding and predicting IL properties. The ionisation energies of 60 ILs are measured and the most readily ionised valence state of each IL (the highest occupied molecular orbital, HOMO) is identified using a combination of X-ray photoelectron spectroscopy (XPS) and synchrotron resonant XPS. A structurally diverse range of cations and anions were studied. The cation gave rise to the HOMO for nine of the 60 ILs presented here, meaning it is energetically more favourable to remove an electron from the cation than the anion. The influence of the cation on the anion electronic structure (and vice versa) were established; the electrostatic effects are well understood and demonstrated to be consistently predictable. We used this knowledge to make predictions of both ionisation energy and HOMO identity for a further 516 ILs, providing a very valuable dataset for benchmarking electronic structure calculations and enabling the development of models linking experimental valence electronic structure descriptors to other IL properties, e.g. electrochemical stability. Furthermore, we provide design rules for the prediction of the electronic structure of ILs.

A combined density functional theory and x-ray photoelectron spectroscopy study of the aromatic amino acids

Amino acids are essential to all life. However, our understanding of some aspects of their intrinsic structure, molecular chemistry, and electronic structure is still limited. In particular the nature of amino acids in their crystalline form, often essential to biological and medical processes, faces a lack of knowledge both from experimental and theoretical approaches. An important experimental technique that has provided a multitude of crucial insights into the chemistry and electronic structure of materials is x-ray photoelectron spectroscopy. While the interpretation of spectra of simple bulk inorganic materials is often routine, interpreting core level spectra of complex molecular systems is complicated to impossible without the help of theory. We have previously demonstrated the ability of density functional theory to calculate binding energies of simple amino acids, using ΔSCF implemented in a systematic basis set for both gas phase (multiwavelets) and solid state (plane waves) calculations. In this study, we use the same approach to successfully predict and rationalise the experimental core level spectra of phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), and histidine (His) and gain an in-depth understanding of their chemistry and electronic structure within the broader context of more than 20 related molecular systems. The insights gained from this study provide significant information on the nature of the aromatic amino acids and their conjugated side chains.

Synergistic effect of hematite facet and Pd nanocluster for enhanced acetylene dicarbonylation

It is very challenging to improve the catalytic activity of Pd-based catalysts since the strong CO chemisorbtion on Pd leading to poor activity at ambient temperature. Herein, we report that modulating the exposed facet of α-Fe2O3 nanocrystalline, i.e. (110), (001) and (012), is a facial way to improve catalytic activity for acetylene dicarbonylation. The obtained Pd/HNRs catalyst with exposed (110) crystal plane give a 100 % acelyene conversion at room temperature. Through a combination of X-ray photoelectron spectroscopy and H2-TPR, we demonstrate that the Pd-HNRs interaction leads to the weaker CO absorption strength. Meanwhile, the kinetics studies demonstrate that α-Fe2O3 oxide extends the reaction routine due the improved activity of C2H2, with the help of moderately acidic sites, then overcome the inhibition of the C2H2 activating in pure Pd species. Moreover, we verified a satisfying reusability over the Pd/HNRs catalyst, being used in up to eight consecutive cycles without loss of activity or selectivity significantly.