XPS Binding Energy Research Articles

Mechanochemical Synthesis of Non-Solvated Dialkylalumanyl Anion and XPS Characterization of Al(I) and Al(II) Species.

A non-solvated alkyl-substituted Al(I) anion dimer was synthesized by a reduction of haloalumane precursor using a mechanochemical method. The crystallographic and theoretical analysis revealed its structure and electronic properties. Experimental XPS analysis of the Al(I) anions with reference compounds revealed the lower Al 2p binding energy corresponds to the lower oxidation state of Al species. It should be emphasized that the experimentally obtained XPS binding energies were reproduced by delta SCF calculations and were linearly correlated with NPA charges and 2p orbital energies.

Intramolecular O···H Hydrogen Bonding of Salicylic Acid: Further Insights from O 1s XPS and 1H NMR Spectra Using DFT Calculations.

Intramolecular hydrogen bonding (HB) is a complex phenomenon that extends beyond a simple valence event, affecting the core electrons of a molecule. Salicylic acid (SA) and its conformers provide an excellent model compound for studying intramolecular HB as the proton donor (H) and acceptor (O) can be toggled by rotating the C-O and C-C bonds to form up to seven potential conformers through various HB. In this study, we computationally investigated intramolecular interactions in SA conformers with and without such HB, by examining their calculated O 1s core electron-binding energy (CEBE) and 1H NMR chemical shifts validated using recent measurements. The quantum mechanically stable SA conformers are fully defined by three rotatable bonds in the compound, which are abstracted as SA(η1η2η3) digital structures, where ηi = 0 if the ηi angles match the most stable SA conformer (000) and ηi = 1 otherwise. Our findings suggest that the stability is dominated by the appearance of the intergroup intramolecular HB of Hp···O (where O is in the carboxylic acid functional group and Hp is the phenolic proton in -OHp), and η3 serves as a switch of such HB. As a result, the (η1η20) SA conformers containing such Hp···O HB are more stable than other SA conformers (η1η21) without such the Hp···O HB. The present density functional theory calculations reveal that this Hp···O HB results in splitting of the O 1s CEBEs of two hydroxyl groups (-OH) by up to 1 eV and deshielding the Hp proton 1H NMR (δHp) up to 11.68 ppm for the (η1η20) conformers. Without such Hp···O HB, the O 1s XPS binding energies of two -OH groups will be closely located in the same band, and the 1H NMR chemical shift of the Hp atom will be as small as an 4.09 ppm SA conformer [SA-G(101)]. The present study indicates that the O 1s CEBE splitting between two -OH groups serves as an indicator of the presence of the Hp···O HB in SA conformers, which is also supported by the 1H NMR results.

Template-free self-assembly of mesoporous ZnO nanocluster/ polymethyl methacrylate based anisotropic nanocomposite thin films with enhanced interfacial interactions and tuneable optical properties

Nature inspired biomimetic growth of anisotropic, hierarchical nanostructures could offer insight into new and exciting crystalline properties for advanced multifunctional applications. Our study demonstrates diethanolamine-mediated mesoscopic self-assembly of semiconducting ZnO Quantum Dots (3–5 nm) into lattice-aligned, symmetrical superstructures (40–50 nm) via non-classical oriented attachment (OA) crystal growth observed in various biomineralization processes. Multifunctional nanocomposite thin films of self-assembled nanostructures and polymethyl methacrylate were spin-coated onto plasma-treated Si wafers and the surface and interfacial properties were rigorously studied. HR-TEM images depicted the OA growth process with neighboring nano-crystals having perfectly aligned lattices. Preferential orientation of the thin films along <100> direction was evident from the XRD data. Quantum confinement in ZnO QDs and surface defect originating sharp green PL emission were examined through UV–Vis absorption and Photoluminescence spectra respectively. DLS and Zeta potential studies of surface-engineered colloidal superstructures established excellent long-term physico–chemical stability with no agglomeration or transparency loss observed in ZnO mesocrystal suspension even after 6 months. Diethanolamine, due to its dual functionality radically enhanced the interaction between polar ZnO and non-polar PMMA matrix resulting in highly stable thin films (Class II hybrids) with enhanced surface and interfacial properties as evident from the extremely low surface roughness and homogenous nanofiller dispersion observed in AFM and FE-SEM studies. Chemical interactions at the interface were also established quantitatively by XPS binding energy measurements which suggested hydrogen bonds and covalent bonds between organic-inorganic phases promoted via diethanolamine surface engineering.

Cobalt complexes with multi-dentate N-donor ligands: Redox, X-ray photoelectron spectroscopic and theoretical study

Five CoII complexes were prepared with different multi-dentate N-donor ligands (5-Nitro-1,10-phenanthroline, 1,10-phenanthroline, 2,2′:6′,2″-terpyridine, 2,2′-dipyridyl or 4,4′-dimethoxy-2,2′-bipyridine). Complexation was confirmed with the blue-shift of stretching frequency of the CN moiety of the ligands as measured by ATR FTIR and by XPS spectra. The average XPS binding energies (BE) of the main and satellite structures of Co 2p3/2 photoelectron lines for CoII were ca. 780.3 eV and 785.0 eV respectively. The diffusion controlled formal reduction potential E0′ of the CoII/III redox couple measured in aqueous medium ranged between 0.08 and 0.58 V versus NHE. Ihe CoII/I redox couple measured in DMF ranged between between −1.1 and −1.7 V vs HFc/HFc+. Directly proportional relationships were established between the E0′ of both the CoII/III and CoII/I redox couples and the BE of the main CoII 2p3/2 photoelectron lines and DFT calculated energies and charges. These relationships all illustrate the electronic influence of the different N-donor ligands on the effective charge of the central cobalt(II) ion the ligands are coordinated to, can be quantised by the different experimental redox and XPS BE values and DFT calculated electronic descriptors.

Hierarchical Nanoflowers of MgFe2O4, Bentonite and B-,P- Co-Doped Graphene Oxide as Adsorbent and Photocatalyst: Optimization of Parameters by Box-Behnken Methodology.

In the present study, nanocomposites having hierarchical nanoflowers (HNFs) -like morphology were synthesized by ultra-sonication approach. HNFs were ternary composite of MgFe2O4 and bentonite with boron-, phosphorous- co-doped graphene oxide (BPGO). The HNFs were fully characterized using different analytical tools viz. X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersion spectroscopy, transmission electron microscopy, X-ray diffraction, vibrating sample magnetometry and Mössbauer analysis. Transmission electron micrographs showed that chiffon-like BPGO nanosheets were wrapped on the MgFe2O4-bentonite surface, resulting in a porous flower-like morphology. The red-shift in XPS binding energies of HNFs as compared to MgFe2O4-bentoniteand BPGO revealed the presence of strong interactions between the two materials. Box–Behnken statistical methodology was employed to optimize adsorptive and photocatalytic parameters using Pb(II) and malathion as model pollutants, respectively. HNFs exhibited excellent adsorption ability for Pb(II) ions, with the Langmuir adsorption capacity of 654 mg g−1 at optimized pH 6.0 and 96% photocatalytic degradation of malathion at pH 9.0 as compared to MgFe2O4-bentonite and BPGO. Results obtained in this study clearly indicate that HNFs are promising nanocomposite for the removal of inorganic and organic contaminants from the aqueous solutions.

Roles of Al2O3 coating layer on an ordered mesoporous Ni/m-Al2O3 for combined steam and CO2 reforming with CH4

To enhance catalytic and thermal stability of Ni nanoparticles for a combined steam and CO2 reforming with CH4 (CSCR), the utilization of an ordered mesoporous Al2O3 support with ∼6 nm of average pore diameter (Ni/m-Al) was proposed in terms of spatial confinement effects of the Ni nanoparticles with the help of successive Al2O3 overlayer protective layers (Ni/m-Al@Al). At an optimal amount of Al2O3 coating layers less than ∼3 wt%, the much higher catalytic activity and stability were observed on the Ni/m-Al@Al(3). The synergy effects of Al2O3 overlayers on the ordered mesoporous Ni/m-Al were mainly attributed to the formation of strongly interacted Ni-Al2O3 interfaces as supported by its higher XPS binding energy in the spatially restricted mesoporous m-Al channels with the protective metal oxide overlayers. Those structures were also responsible for the suppressed migrations of the spatially confined Ni nanoparticles to the outer m-Al surfaces by Al2O3 protective overlayers, which resulted in an excellent long-term stability with small coke depositions by preserving the original Ni nanoparticle sizes.

Bio-enrichment of heavy metals U(VI) in wastewater by protein DSR A.

Uptaking U(VI) from the environment by biological method is an environmental friendly and efficient way. In this work, we have acquired and isolated the protein DSR A by genetic engineering, then assessed its capacity and mechanisms to absorb U(VI) from wastewater. As results, we proved that protein DSR A can precisely recognize, enrich and remove uranyl ions in simulated wastewater solution. Its great removal potential was demonstrated in the adsorption experiments, the adsorption capacity of protein DSR A can reach 182.3mg/g in the condition at 10mg/L U(VI) and pH = 6. The Langmuir isotherm model and the pseudo-first-order kinetic equation were used to better describe the absorption process. We can confirm that Na+, Sr2+ and K+, these three metal ions have less effect on the enrichment of U(VI) by protein DSR A compared with other common cations. Besides, we can educe some mechanisms for the removal of U (VI) by protein DSR A from the results of FTIR, SEM-EDS, XPS (binding energy = 2.0 ~ 4.0ke V), MAP and XRD analysis before and after adsorption. This work has demonstrated the great potential of genetic engineering and biological methods in dealing with environmental heavy ion pollution.

XPS binding energy shifts as a function of bond distances: a case study of CO

The O(1s) and C(1s) XPS core-level binding energies. BEs, have been studied as a function of the C–O internuclear distance for a large range of distances. The BE(r) for both BEs show considerable variation over the distances studied which is, however, different for the O(1s) and C(1s) BEs. The origin of the dependence on C–O distance is established and shown to involve more than the electric field generated because of the charge separation within CO being C+q and O−q . Furthermore, the BE(r) is shown to be different for Hartree–Fock and correlated wavefunctions indicating that the BE(r) can provide evidence of how electron correlation modifies the valence charge distribution. The difference between the O(1s) and C(1s) BEs is examined and it is proposed that this difference can be used as a measure of the accuracy of theoretically predicted BEs. It is believed that the features found for CO may be representative for the BE variations with geometry for other systems; an effect that has been mostly overlooked.

First-principles study of absolute XPS binding energy with PAW planewave pseudopotential method: application to tungsten disulfides

We propose an efficient theoretical method to take into account the core-hole spin density in the projector augmented wave method, combined with spin un-polarized pseudopotentials and the planewave basis set. We apply this method to the calculation of absolute core level X-ray photoelectron spectroscopy binding energies of WS2 and its related materials, and find the following points. First, inclusion of core-hole spin in the core-exited state is essential for accurate description of the binding energies, especially for light elements. Second, the calculated absolute binding energies show excellent agreement with experimental results. Finally, when oxygen atoms are incorporated in the basal plane of WS2 in the metallic phase, the O 1s binding energy is expected to appear at lower energy than the corresponding value in the semiconducting phase.

Many-body effects for the Mg 2s XPS of MgO

The energy separation of the higher lying cation XPS binding energies, BEs, for MgO is examined. It is shown that the Hartree–Fock BEs overestimate the separation of the Mg BE(2s) and BE(2p), because an important many-body effect is neglected in the determination of the Hartree–Fock BEs. Once the many-body effect is taken into account, there is good agreement between theory and the XPS measurement. The character of this atomic many-body effect is established in terms of a nearly degenerate configuration that is needed to describe the wavefunction when an Mg 2s electron is ionized. The results provide additional evidence of the ionic character of the MgO crystal. Given the atomic character of the many-body effect, it is likely to apply also to the BE separations of other closed shell oxides.

C[sbnd]F bonding in fluorinated N-Doped carbons

Porous carbons are used in various applications for energy storage. Nitrogen doping of these carbons modifies their electrochemical and chemical properties and co-doping them with fluorine atoms, appears as a promising route to further tailor their physical and chemical properties. The present paper focuses on the gas/solid fluorination with molecular fluorine (F2) of various types of N-doped porous carbons. The consequences of the fluorination on the porosity of these materials were studied as well as their CF bonding type. Mild conditions avoid a huge decomposition in F2 gas of these materials and a drastic decrease of their specific surface area. Micropores, which are hosting most of the FeNx catalytic sites, are the most affected by fluorination, and a new N1s XPS peak assigned to pyridinic-N---CF has been identified, coinciding with that of the XPS binding energy of N1s in FeNx. However, molecular fluorine did not react directly with nitrogen atoms in these materials, whatever their type since no NF containing volatile products were evolved during the treatment. Finally, a dual CF bonding, characterized by the coexistence of CF bonds with weakened covalence and covalent CF, is evidenced in all fluorinated N-doped porous carbons.

Reaction mechanism and kinetics for CO2 reduction on nickel single atom catalysts from quantum mechanics

Experiments have shown that graphene-supported Ni-single atom catalysts (Ni-SACs) provide a promising strategy for the electrochemical reduction of CO2 to CO, but the nature of the Ni sites (Ni-N2C2, Ni-N3C1, Ni-N4) in Ni-SACs has not been determined experimentally. Here, we apply the recently developed grand canonical potential kinetics (GCP-K) formulation of quantum mechanics to predict the kinetics as a function of applied potential (U) to determine faradic efficiency, turn over frequency, and Tafel slope for CO and H2 production for all three sites. We predict an onset potential (at 10 mA cm−2) Uonset = −0.84 V (vs. RHE) for Ni-N2C2 site and Uonset = −0.92 V for Ni-N3C1 site in agreement with experiments, and Uonset = −1.03 V for Ni-N4. We predict that the highest current is for Ni-N4, leading to 700 mA cm−2 at U = −1.12 V. To help determine the actual sites in the experiments, we predict the XPS binding energy shift and CO vibrational frequency for each site.

Orbitals Permit the Interpretation of Core-Level Spectroscopies in Terms of Chemistry

We present evidence that the use of orbital based analyses provides an important fundamental basis for interpreting and understanding the significance of features in core-level spectroscopies, in particular, X-ray photoelectron spectroscopy, XPS. A recent paper by Truhlar and colleagues cautions about the limitations of orbital based interpretations of photoelectron spectroscopy for the accurate modeling of the electronic structure of the ions. We provide an alternate view that does use orbitals to derive detailed information from XPS. We discuss the appropriate meaning of Koopmans’ theorem as a way to separate the chemically interesting initial state contributions to XPS binding energies, BEs, from the less interesting properties of highly excited ionic states, rather than as a way to estimate values of BEs and BE shifts. The use of orbitals and orbital occupations to take into account the spin and orbital angular momentum coupling that leads to the observed XPS multiplets is shown to be important to understand the number and energy spread of XPS features. The use of a standard approximation to determine the XPS intensities, essential for the theoretical prediction of XPS spectra, is shown to depend on the concept of ionization of electrons from specific orbitals. Finally, the use of orbital properties to identify and include the main many electron correlation of the ionic states in XPS is described. The importance of these considerations is shown by describing examples where they are used in the theoretical determination and the theoretical analysis of the XPS of representative systems. The orbital description of XPS is shown schematically below for the Ne atom. An orbital description can be applied to and is appropriate to understand the photoemission of complex systems.

Photocatalytic hydrogen production using bench-scale trapezoidal photocatalytic reactor

Hydrogen is the future fuel and energy carrier, which has numerous applications. During combustion, produces only water vapour instead of greenhouse gas emissions. Photocatalytic production of hydrogen as a clean fuel from sulphide wastewater arises as a necessary option that must be considered. Here we report the performance of CNT added CdZnS/Fe2O3 for hydrogen recovery from highly toxic sulphide containing wastewater. The prepared photocatalysts were characterised for XRD (structure), UV-DRS (band gap), HRTEM (particle size), XPS (binding energy), SEM (morphology) and ICP (elemental composition). The photocatalytic hydrogen recovery was performed using novel trapezoidal photocatalytic reactor. The synthesized novel CNT - CdZnS/Fe2O3 nano-photocatalyst has highest production of hydrogen (2679 μmol/h) than plain CdZnS/Fe2O3 (2009 μmol/h).The feasibility studies were conducted to optimize the operating variables viz., S2- (sulphide ion) concentrations, SO32- (sulphite ion) concentrations, catalyst amount, light irradiation and volume of wastewater. Reusability studies under natural solar irradiation were performed and the CNT deposited CdZnS/Fe2O3 photocatalyst was found to be stable upto seven runs.

Hematite-catalysed scorodite formation as a novel arsenic immobilisation strategy under ambient conditions

Scorodite is an important mineral not only for arsenic (As) removal from industrial wastewaters but also in the mobility and final fate of As in waste rocks, contaminated soils and sediments, and mine tailings. Because of the mineral's high As-loading capacity and stability, numerous studies have been done to understand its formation. Unfortunately, most of these studies were limited to elevated temperatures (>70 °C), so the processes involved in scorodite formation under ambient conditions remain unclear. This study provides evidence of the catalytic effects of hematite on the formation of scorodite at 25 °C in a pyrite-rich natural geologic material. Scorodite peaks were detected in the XRD patterns of the leaching residues with and without hematite, but those in the former were stronger and more pronounced than the latter. These results suggest that the formation of scorodite was catalysed by hematite, a generalisation that is further supported by strong characteristic IR absorption bands of scorodite at 819 cm–1 (As–O bending vibration), 785 and 725 cm–1 (As–O stretching vibrations), and 2990 cm−1 (OH-vibration) as well as the distinct XPS binding energies of Fe(III)–As (709.7 eV), As(V)–O (44.8, 44.31 and 43.7 eV), O2− (530.5 eV) and coordinated water (531.3 eV) in scorodite. This phenomenon could be attributed to three possible mechanisms: (1) more rapid precipitation promoted by the “seeding” effect of hematite particles, (2) additional supply of Fe3+ from hematite dissolution under acidic conditions, and (3) enhanced oxidations of Fe2+ to Fe3+ and As(III) to As(V) on the surface of hematite.

Low temperature chemical vapor deposition of superconducting vanadium nitride thin films

Superconducting thin films of vanadium nitride have been grown by low temperature (250–300 °C) chemical vapor deposition from tetrakis(dimethylamido)vanadium (TDMAV) and ammonia. For example, films grown from TDMAV (1 sccm Ar as carrier gas) and 7 mTorr ammonia at 300 °C are nanocrystalline (cubic δ-phase) with an average crystal size of 20 nm, have relatively low room temperature resistivities of 250 μΩ cm, and are superconducting with critical temperatures as high as 7.6 K (versus a bulk value of 9 K). The films have a V:N ratio of 1:1, with a carbon content of &amp;lt;5 at. % and an oxygen content of &amp;lt;3 at. % (as determined by high resolution XPS). The V 2p3/2 and N 1 s XPS binding energies of 513.5 and 397.3 eV, respectively, are consistent with the presence of a nitride phase. In contrast, films grown at lower temperatures &amp;lt;200 °C show carbon incorporation, have a much higher resistivity of ∼3000 μΩ cm, and are not superconducting. The results suggest that, at low temperatures, the thermally activated transamination reaction with ammonia becomes too slow to remove dimethylamido groups from the surface, resulting in carbon-rich films (10–15 at. % carbon). The conformal step coverage of the VN films depends on the growth conditions. For thermal growth of nonsuperconducting films at 150 °C, the step coverage is &amp;gt;95% in trenches of an aspect ratio of 4:1; for superconducting films grown at 250 °C, the step coverage is 65% for an aspect ratio of 3:1. At 150 °C, near-stoichiometric films with &amp;lt;2 at. % carbon and &amp;lt;3 at. % oxygen can be deposited if the gaseous ammonia is precracked by a remote plasma source; the resulting films have low resistivities of 320 μΩ cm but are not superconducting down to 4 K.

Bimetallic Co-Mn Perovskite Fluorides as Highly-Stable Electrode Materials for Supercapacitors.

Bimetallic Co-Mn perovskite fluorides (KCox Mn1-x F3 , denoted as K-Co-Mn-F) with various Co/Mn ratios (1:0, 12:1, 6:1, 3:1, 1:1, 1:3, 0:1) were prepared through a one-pot solvothermal strategy and further used as electrode materials for supercapacitors. The optimal K-Co-Mn-F candidate (Co/Mn=6:1) showed a size range of 0.1-1 μm and uniform elemental distribution; exhibiting small changes in XRD peaks and XPS binding energy in comparison to the bare K-Co-F and K-Mn-F, due to the structural/electronic effects. Owing to the stronger synergistic effect of Co/Mn redox species, the K-Co-Mn-F (Co/Mn=6:1) electrode exhibited superior specific capacity and rate behavior (113-100 C g-1 at 1-16 Ag-1 ) together with excellent cycling stability (118 % for 5000 cycles at 8 Ag-1 ), and the activated carbon (AC)//K-Co-Mn-F (Co/Mn=6:1) asymmetric capacitor showed superior energy and power densities (8.0-2.4 Wh kg-1 at 0.14-8.7 kW kg-1 ) along with high cycling stability (90 % for 10 000 cycles at 5 Ag-1 ).

Significance of the electron-density of molecular fragments on the properties of manganese(iii) β-diketonato complexes: an XPS and DFT study

The group electronegativity of the R-groups of the ligand influences the XPS binding energies and the amount of charge transferred in the Mn 2p3/2photoelectron lines. DFT studies illustrated different Jahn–Teller elongation bond stretch isomers.

Consequences of electron correlation for XPS binding energies: Representative case for C(1s) and O(1s) XPS of CO.

In this paper, we present a study of the signs and the magnitudes of the errors of theoretical binding energies, BE's, of the C(1s) and O(1s) core-levels compared to BE's measured in X-Ray photoemission, XPS, experiments. In particular, we explain the unexpected sign of the error of the Hartree-Fock C(1s) BE, which is larger than experiment, in terms of correlation effects due to the near degeneracy of the CO(1π) and CO(2π) levels and show how taking this correlation into account leads to rather accurate predicted BE's. We separate the initial state contributions of this near degeneracy, present for the ground state wavefunction, from the final state near degeneracy effects, present for the hole state wavefunctions. Thus, we are able to establish the importance for the core-level BE's of initial state charge redistribution due to the π near-degeneracy. While the results for CO are interesting in their own right, we also consider whether our conclusions for CO are relevant for the analysis of XPS spectra of a wider range of molecules.

Studies on Ni–M (M = Cu, Ag, Au) bimetallic catalysts for selective hydrogenation of cinnamaldehyde

Bimetallic catalysts of the type Ni–M with M=Cu, Ag and Au, and supported on TiO2-P-25 have been prepared by chemical reduction using glucose as the reducing agent. Hydrogenation of cinnamaldehyde (CAL) to yield hydrocinnamaldehyde (HCAL), cinnamyl alcohol (COL) and hydrocinnamyl alcohol (HCOL) has been studied on the catalysts in the temperature range 60–140°C and at 20kg/cm2 pressure, with methanol as solvent. Ni crystallite sizes, measured by X-ray line broadening analysis (XLBA), H2 pulse chemisorption and Transmission Electron Microscope (TEM) techniques, are in the range 8–12nm. Temperature Programmed Reduction (TPR) and Diffuse Reflectance Spectroscopic (DRS) studies indicate the formation of Ni–Cu alloys, while Ni–Ag and Ni–Au exist as bimetallic nanoparticles. High-resolution HRTEM studies show that the bimetallic nanoparticles are in close contact, forming hetero junctions. Changes in the XPS binding energy values for Ni 2p1/2 and Ni 2p3/2 levels reveal that Cu/Ag/Au, tend to increase electron density around Ni, which retards the adsorption of CAL via olefinic bond and weakens NiH bond strength. H2 TPD measurements also indicated weakening of NiH bond. Bimetallic catalysts display higher CAL conversion and selectivity to COL vis-à-vis the corresponding monometallic catalysts at lower reaction temperatures, 60–80°C. But, selectivity to COL decreases at higher temperatures, 100–120°C. Mode of adsorption of CAL and nature of adsorbed hydrogen on bimetallic catalysts influence their activity and selectivity.