X-ray Photoelectron Spectroscopy Studies Research Articles

Nanoengineered Cobalt Electrocatalyst for Alkaline Oxygen Evolution Reaction

The alkaline oxygen evolution reaction (OER) remains a bottleneck in green hydrogen production owing to its slow reaction kinetics and low catalytic efficiencies of earth abundant electrocatalysts in the alkaline OER reaction. This study investigates the OER performance of hierarchically porous cobalt electrocatalysts synthesized using the dynamic hydrogen bubble templating (DHBT) method. Characterization studies revealed that electrocatalysts synthesized under optimized conditions using the DHBT method consisted of cobalt nanosheets, and hierarchical porosity with macropores distributed in a honeycomb network and mesopores distributed between cobalt nanosheets. Moreover, X-ray photoelectron spectroscopy studies revealed the presence of Co(OH)2 as the predominant surface cobalt species while Raman studies revealed the presence of the cubic Co3O4 phase in the synthesized electrocatalysts. The best performing electrocatalyst required only 360 mV of overpotential to initiate a current density of 10 mA cm−2, exhibited a Tafel slope of 37 mV dec−1, and stable OER activity over 24 h. The DHBT method offers a facile, low cost and rapid synthesis approach for preparation for highly efficient cobalt electrocatalysts.

Ni Single Atom Decorated Porous Hollow Carbon Nanosphere-Based Electrodes for High Performance Symmetric Solid-State Supercapacitors.

Ni single atom containing hollow carbon nanospheres with nitrogen doping has been synthesized by carbonization of Ni(NO3)2/phloroglucinol-formaldehyde polymer/silica composite. The samples have been characterized by powder X-ray diffraction, nitrogen adsorption/desorption, electron microscopic, Raman and X-ray photoelectron spectroscopic studies. The microstructure and surface area vary with the amount of Ni(NO3)2 employed in the syntheses and the carbonization environment. An optimized amount of nickel and argon as the carbonization gas afford Ni-1.0@N@HCN-Ar which possesses overall superior features. The uniformly dispersed Ni single atoms within the hollow porous carbon framework fully utilize all the electroactive sites thereby improving the supercapacitive performance. The specific capacitance of Ni-1.0@N@HCN-Ar reaches 777 F∙g-1 at 1 A∙g-1 with a Coulombic efficiency of 98.4% and excellent recyclability. The energy and power density of Ni-1.0@N@HCN-Ar are found to be high; at 1 A∙g-1 its energy density is 155.4 Wh∙kg-1 with a power density of 600.3 W∙kg-1. At a high current density of 10 A∙g-1 the material shows a high energy density of 118.4 Wh∙kg-1 with excellent power density of 6003.4 W∙kg-1. A symmetric solid-state supercapacitor assembled with this material, Ni-1.0@N@HCN-Ar//Ni-1.0@N@HCN-Ar using H2SO4/PVA gel electrolyte shows a superior energy density value of 30 Wh∙kg-1 at a power density of 1200 W∙kg-1.

Charge Transfer Mechanism on a Cobalt-Polyoxometalate-TiO2 Photoanode for Water Oxidation in Acid.

We constructed a photoanode comprising the homogeneous water oxidation catalyst (WOC) Na8K8[Co9(H2O)6(OH)3(HPO4)2(PW9O34)3] (Co9POM) and nanoporous n-type TiO2 photoelectrodes (henceforth "TiO2-Co9POM") by first anchoring the cationic 3-aminopropyltrimethoxysilane (APS) ligand on a metal oxide light absorber, followed by treatment of the metal oxide-APS with a solution of the polyoxometalate WOC. The resulting TiO2-Co9POM photoelectrode exhibits a 3-fold oxygen evolution photocurrent enhancement compared to bare TiO2 in aqueous acidic conditions. Three-element (Co 2p, W 4f, and O 1s) X-ray photoelectron spectroscopy and Raman spectroscopy studies before and after use indicate that surface-bound Co9POM retains its structural integrity throughout all photoelectrochemical water oxidation studies reported here. Extensive charge-transfer mechanistic studies by photoelectrochemical techniques and transient absorption spectroscopy elucidate that Co9POM serves as an efficient WOC, extracting photogenerated holes from TiO2 on the picosecond time scale. This is the first comprehensive mechanistic investigation elucidating the roles of polyoxometalates in POM-photoelectrode hybrid oxygen evolution reaction systems.

Designing a Phenalenyl-Based Dinuclear Ni(II) Complex: An Electrocatalyst with Two Single Ni Sites for the Oxygen Evolution Reaction (OER).

A new dinuclear Ni(II) complex 1, [Ni2II(dtbh-PLY)2], is synthesized from 9-(2-(3,6-di-tert-butyl-2-hydroxybenzylidene)hydrazineyl)-1H-phenalen-1-one, dtbh-PLYH2 ligand, and structurally characterized by various analytical tools including the single-crystal X-ray diffraction (SCXRD) technique. In the solid state, both Ni(II) metal centers in complex 1 exist in a distorted square planar geometry and display the presence of rare Ni···H-C anagostic interactions to form a one-dimensional (1-D) linear motif in the supramolecular array. Complex 1 is further stabilized in the solid state by π-π-stacking interactions between the highly delocalized phenalenyl rings. The redox features of complex 1 have been analyzed by the cyclic voltammetry (CV) technique in solution as well as in the solid state, revealing the crucial involvement of both the Ni(II) metal centers for undergoing quasi-reversible oxidation reactions on the application of an anodic sweep. A complex 1-modified glassy carbon electrode, GC-1, is employed as an electrocatalyst for oxygen evolution reaction (OER) in 1.0 M KOH, giving an OER onset at 1.45 V, and very low OER overpotential, 300 mV vs the reversible hydrogen electrode (RHE) to reach 10 mA cm-2 current density. Furthermore, GC-1 displayed fast OER kinetics with a Tafel slope of 40 mV dec-1, a significantly lower Tafel slope value than those of previously reported molecular Ni(II) catalysts. In situ electrochemical experiments and postoperational UV-vis, Fourier transform infrared (FT-IR), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) studies were performed to analyze the stability of the molecular nature of complex 1 and to gain reasonable insights into the true OER catalyst.

The adsorption of U(VI) on chlorite: batch, modeling and XPS study

Abstract A mechanistic modelling of the adsorption processes onto individual minerals presenting in the near- and far-fields can greatly enhance the credibility of long-term safety assessments of granite-based geological repositories. In this study, the titration and U(VI) adsorption characteristics of chlorite, one of the major minerals of rock fractures, have been studied. Potentiometric titration curves at two ionic strengths (0.1 and 0.4 mol/L NaCl) are successfully interpreted by considering protonation/deprotonation reactions on generic edge sites (≡SOH) in the framework of a non-electrostatic surface complexation model (SCM). The adsorption of U(VI) on chlorite was reached after 24 h, the adsorption kinetics can be described by a pseudo-second-order model. A non-electrostatic SCM with three surface complexes (≡SOUO2 +, ≡SO(UO2)3(OH)5 and ≡SO(UO2)3(OH)7 2−) was set up based on pH edges of U(VI) at adsorption equilibrium in the absence of CO2. Additional, experimental data measured as a function of U(VI) concentration, solid-to-liquid ratio and carbonate concentration were well reproduced by the proposed model. Finally, parallel experiments were conducted using X-ray photoelectron spectroscopy (XPS) to analyze the variation of U(VI) surface species speciation at different pH values. The good agreement between SCM prediction and XPS analysis demonstrates the reliability of the model in predicting and quantifying the radionuclides retention by chlorite.

Insights into Plastic Degradation Processes in Marine Environment by X-ray Photoelectron Spectroscopy Study.

The present study employs X-ray photoelectron spectroscopy (XPS) to analyze plastic samples subjected to degradation processes with the aim to gain insight on the relevant chemical processes and disclose fragmentation mechanisms. Two model plastics, namely polystyrene (PS) and polyethylene (PE), are selected and analyzed before and after artificial UV radiation-triggered weathering, under simulated environmental hydrodynamic conditions, in fresh and marine water for different time intervals. The object of the study is to identify and quantify chemical groups possibly evidencing the occurrence of hydrolysis and oxidation reactions, which are the basis of degradation processes in the environment, determining macroplastic fragmentation. Artificially weathered plastic samples are analyzed also by Raman and FT-IR spectroscopy. Changes in surface chemistry with weathering are revealed by XPS, involving the increase in chemical moieties (hydroxyl, carbonyl, and carboxyl functionalities) which can be correlated with the degradation processes responsible for macroplastic fragmentation. On the other hand, the absence of significant modifications upon plastics weathering evidenced by Raman and FT-IR spectroscopy confirms the importance of investigating plastics surface, which represents the very first part of the materials exposed to degradation agents, thus revealing the power of XPS studies for this purpose. The XPS data on experimentally weathered particles are compared with ones obtained on microplastics collected from real marine environment for investigating the occurring degradation processes.

Staggered band alignment – direct Z-scheme for photocatalytic activity in Stibnite/rGO layered nanohybrids

Type-II staggered band aligned layered nanohybrids (LNHs) satisfy the unique characteristics required for photocatalysts. Here, the spin-assisted layer-by-layer deposition (SA-LBL) of stibnite/reduced graphene oxide (Sb2S3/rGO) LNHs are fabricated and their structural, morphological, electrical, and optical properties are reported. From the FESEM analysis, it was found that with increasing rGO content, the morphology of Sb2S3 nanoparticles changed from the granular to nanorods which might be due to Ostwald ripening or microstructural coarsening effect. Further, Raman spectroscopy proves that the B1 g and Ag of Sb2S3 decrease by the addition of rGO mainly due to the electron-phonon interaction. Based on the estimation of valence band edge and conduction band edge of Sb2S3/rGO LNHs using X-ray photoelectron spectroscopy and optical studies, we propose that the interface in Sb2S3/rGO LNHs is a type-II staggered band alignment Direct Z-scheme. The increased spatial charge separation and carrier lifetime of Sb2S3/rGO LNHs materials results in opening a new pathway to explore and extend their applications as photocatalysts.

Quantitative analysis of molecular interactions in κ-carrageenan-Isovanillin biocomposite for biodegradable packaging and pharmaceutical applications using NMR, TOF-SIMS, and XPS approach

This study explores the molecular interactions and structural changes in κ-carrageenan crosslinked with isovanillin to create a biocomposite material suitable for hard capsule and bio-degradable packaging applications. Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy revealed chemical changes in the conjugate molecule, indicating improved electronegativity due to intermolecular hydrogen bonding between κ-carrageenan and isovanillin. Time-of-flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis revealed enhanced ion intensity due to intermolecular interactions, particularly between sulphate and hydrogen ions. X-ray Photoelectron Spectroscopy (XPS) study demonstrated that κ-carrageenan and isovanillin form stronger hydrogen bonds, with a shift in binding energy indicating higher electronegativity. These findings shed light on the molecular mechanisms that underpin the formation of the biocomposite material, as well as its potential for use in hard capsule and biodegradable packaging materials, addressing the need for sustainable alternatives in the pharmaceutical and packaging industries while also contributing to environmental conservation.

Green Energy Generation via Water Splitting by Non-Photocatalytic Process based on Gd Doped Magnesium Ferrite Hydroelectric Cell

This study presents compelling empirical evidence that highlights the notable effect of increased defect concentration on the splitting of water molecules in MgGdxFe2-xO4 hydroelectric cells (HECs), which serve as a promising avenue for environmentally friendly electricity generation. The MgGdxFe2-xO4 (x = 0.00, 0.02, 0.06 and 0.10) series for eco-friendly electricity generation has been successfully synthesized using a facile sol-gel technique. These materials exhibit the characteristic spinel cubic structure with the Fd-3m space group confirmed using Rietveld analysis of X-ray diffraction plots. A maximum strain of 2.06×10-3 was observed in the MgGd0.10Fe1.90O4, indicating the formation of a probable defective structure. Moreover, the X-ray density values decrease with increase in Gd concentration, suggesting an increase in porosity of the samples. Langmuir hysteresis curve follows a typical type IV pattern further consolidating the mesoscopic nature of the materials. Furthermore, the conclusive identification of defects, particularly oxygen vacancies, through Photoluminescence and X-ray Photoelectron Spectroscopic (XPS) studies, holds an utmost importance in facilitating the water dissociation process at room temperature by ferrites. Impedance spectroscopy has been employed to scrutinize the contribution of small polaron hopping-assisted ionic conduction to the observed improved current density. The maximum short circuit output current of 6.8, 10.1, and 13.4mA was achieved for MgGd0.02Fe1.98O4 (GMF-1), MgGd0.06Fe1.94O4 (GMF-2) and MgGd0.10Fe1.90O4 (GMF-3) HECs, respectively. The corresponding open cell voltage values were found to be 0.85V, 0.92V and 0.98V. Off-load peak power output was 5.78mW, 9.29mW, and 13.13mW, respectively. The estimated Gibbs free energy values were -164.02, -177.53, and -189.11 kJ/mol. MgGdxFe2-xO4-based hydroelectric cells possess the advantages of being cost-effective and yielding eco-friendly by-products without reliance on photocatalytic activity, acid/alkali solutions, or electrolytes. The incorporation of Gadolinium (Gd) dopant not only enhances the hydroelectric current but also contributes to sustained current generation over extended periods. The extended operational lifespan of the cell positions it as an excellent candidate for practical applications

One-pot synthesis of AC/ZnO nanocomposites for highly sensitive, repeatable and fast response humidity sensor

A highly sensitive and repeatable humidity sensor that can measure relative humidity at room temperature (25 °C) was fabricated using activated carbon-ZnO (AC/ZnO) nanocomposites. The AC/ZnO nanocomposites with high oxygen vacancies were prepared by a facile one-pot synthesis method through carbonization of ZnCl2-impregnated biomass precursor. The sensor exhibited a better response (96 % at 0.5 V biasing), short response time (17.4 s), and recovery time (32.1 s). The same 96 % relative response at 0.5V biasing for all four consecutive cycles was observed without losing the response-recovery time, indicating excellent repeatability. On the other hand, biomass-derived single-phase activated carbon (AC) did not respond to humidity change at room temperature. The improved humidity sensing in AC/ZnO nanocomposites was ascribed to the synergistic effects of increased oxygen vacancies, increased active sites in the AC phase, and the formation of p–n heterojunction at the composite interface, substantiated with X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) studies. The sensing mechanism of AC/ZnO nanocomposite was discussed based on the enhanced reduction of H2O by adsorbed O2− at AC/ZnO heterojunction, leading to increasing sensor resistance.

Extraction of gamma iron oxide (γ-Fe2O3) nanoparticles from waste can: Structure, morphology and magnetic properties

In this work, the transformation of waste iron cans to gamma iron oxide (γ-Fe2O3) nanoparticles following acid leaching precipitation method along with their structural, surface chemistry, and magnetic properties was studied. Highly magnetic iron-based nanomaterials, maghemite with high saturation magnetization have been synthesized through an acid leaching technique by carefully tuning of pH and calcination temperature. The phase composition and crystal structure, surface morphology, surface chemistry, and surface composition of the synthesized γ-Fe2O3 nanoparticles were explored by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Energy-dispersive X-ray spectroscopy (EDS). The XRD results confirm the cubic spinel structure having crystallite size 26.90–52.15 nm. The XPS study reveals the presence of Fe, O element and the binding energy of Fe (710.31 and 724.48 eV) confirms the formation of γ-Fe2O3 as well. By dynamic light scattering (DLS) method and zeta potential analyzer, the particle size distribution and stability of the systems were investigated. The magnetic behavior of the synthesized γ-Fe2O3 nanoparticles were studied using a vibrating sample magnetometer (VSM) which confirmed the ferrimagnetic particles with saturation magnetization of 54.94 emu/g. The resultant maghemite nanoparticles will be used in photocatalysts and humidity sensing. The net impact of the work stated here is based on the principle of converting waste into useful nanomaterials. Finally, it was concluded that our results can give insights into the design of the synthesis procedure from the precursor to the high-quality gamma iron oxide nanoparticles with high saturation magnetization for different potential applications which are inexpensive and very simple.

Self-assembled complexing agent assisted chemical bath deposition of SnOX enabled highly efficient perovskite solar cells

Chemical bath deposition (CBD) is generally used to fabricate SnOX electron transport layer (ETL) for perovskite solar cells, whereas a lack of understanding of the reaction mechanism hampers further improvement of device performance. Here, we elucidate the reaction mechanism by monitoring the SnOX growth process via a series of advanced X-ray photoelectron spectroscopy studies. For the first time, we successfully modulated the nucleation and crystal growth of SnOX during the CBD process by introducing complexing agent via inherently forming a self-assembled monolayer on the outmost surface of SnOX. The complexing agents can assist the heterogeneous nucleation and crystal growth of SnOX. By a comparison study of different complexing agents, we found that the 2,3-dimercapto-1-propanesulfonate sodium not only assist in achieving a high-quality SnOX ETL, but also serve as a bridge to connect with perovskite via coordination interactions. Leveraging these insights, we achieved a champion efficiency of 24.2 % for perovskite solar cells with ∼ 2300 h stability at ambient condition.

Preparation of a membrane-sealed cell for studying catalyst nanoparticles in flowing gas with high vacuum x-ray photoelectron spectrometer.

Here a sealing-style x-ray photoelectron spectroscopy study of the surface of a 1.0 wt. %Ni/TiO2 nanoparticle catalyst in a flowing mixture of CO and O2 at 1bar was performed with a graphene membrane-sealed Si3N4 window-based miniature cell. We report the details on how a commercial Si3N4 window is modified before assembling a graphene membrane, how single-layer graphene membranes are transferred from their metal supports to the modified Si3N4 window, how a modified Si3N4 window covered with a double-layer graphene membrane is assembled onto a blank cell cap, how a nanoparticle catalyst is introduced to the cell cap and then the cell cap is installed onto a cell body to form a complete reaction cell, and how a complete cell is interfaced with a high vacuum chamber of an XPS system before an XPS study of 1.0 wt. %Ni/TiO2 catalyst surface in a flowing mixture for 0.2bar CO and 0.8bar O2 is performed. How the characterization of a catalyst using this type of graphene membrane-sealed Si3N4 window-based miniature cell is relevant to the finding of the actual surface chemistry of a catalyst during catalysis is discussed.

Improved Near-Resonant Two Photon Absorption of α-MnO2 Nanowires Surface Functionalized Reduced Graphene Oxide Sheets

The versatile study of graphene derivatives has resurgence of interest on understanding its nonlinear optical response at different nanoscales. Nanostructured manganese dioxide: reduced graphene oxide (MnO2: rGO) hybrids were synthesized by reduction method by varying the content of rGO (5, 10, 15 & 20wt%). X-ray Photoelectron Spectroscopy studies confirmed the surface functionalization of MnO2 on rGO. Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Tunnelling Electron Microscopy (HRTEM) witness that with respect to the content of rGO, the morphology of MnO2 varies radically from clusters to nanorods to nanowires over the surface of rGO sheets. Ground state absorption spectra of the hybrids have absorption edge at 268nm corresponding to combined metal oxide charge transfer between rGO (π-π⁎ transition of C=C and n-π transition of C-O bonds) and MnO2 (d-d transition). Moreover, hierarchical MnO2 nanowire network resided on 2D rGO sheets involves broad absorption at the visible spectral domain due to polaron transition as well the localization of π- π⁎ transited electrons that facilitates the probability of occurrence of excited state absorption. Intensity dependent open aperture Z-scan technique of the prepared hybrids using Q-switched Nd: YAG 532nm nanopulsed laser reveals unusual transitions and enhanced nonlinear absorption. MnO2:(5wt%) rGO shows saturable absorption (SA) at low intensity and changeover dynamically to reverse saturable absorption (RSA) at higher intensity. MnO2:(10 & 15wt%) rGO exposes coupled nonlinear absorption (SA + RSA) owing to the combined effect of graphene (π-states) and MnO2 (σ-states). MnO2:(20wt%) rGO exhibits a stronger RSA ascribed to sequential two photon absorption. The third-order nonlinear absorption coefficient and limiting threshold of MnO2: rGO (20wt%) are 4.04 ×10-10m/W and 0.84 ×1012W/m2, which shows five-fold increase compared to bare rGO and MnO2. The obtained results propose that the optical nonlinearity of MnO2 nanowires surface functionalized rGO sheets can significantly be tuned to meet the requirements for fabricating laser safety devices.

XPS Study on the determination of binding energies in high-purity TiO2 nanoparticles

This study focuses on the precise determination of the binding energies of high-purity TiO2 nano-particles, using X-ray photoelectron spectroscopy (XPS). TiO2, an essential ceramic in high-tech sectors such as electronics, aerospace and photocatalysis, was analyzed in its pure state (99.5%) directly as received from the supplier, without previous alterations. XPS spectra revealed typical bond energy peaks for Ti at 458.42 eV and 464.13 eV, corresponding to Ti2p3/2 and Ti2p1/2 levels respectively, with a difference of 5.71 eV, validating the expected electron structure for Ti in TiO2. Additionally, peaks were identified at 457.36 eV and 463.36 eV, attributable to Ti3+, present in a Ti3O5 phase, as confirmed by X-ray diffraction (XRD) analysis. The mid-height width (FWHM) of the main Ti4+ peaks, ranging from 1.08 to 1.87 eV, and 0.96 eV for the Ti3+ peaks, highlights the homogeneity and exceptional purity of the sample. These findings not only corroborate the high quality of TiO2, but also provide a crucial benchmark for the scientific community, facilitating de-tailed comparisons with other samples and encouraging the development of innovative processes and materials. This study underscores the value of the XPS technique in the characterization of advanced ceramic materials and sets a standard for future research.

Acoustic shock wave induced chemical reactions–A case study of NaCl single crystal

Herein, we report the catalytic-free acoustic shock wave-induced synthesis of the non-stoichiometry compound of sodium chloride (Na3Cl2-P4/m) from the stoichiometry NaCl (B1). The shocked NaCl crystal structure is formed as a mixed phase together with the NaCl (B1) and (Na3Cl2-P4/m) thereby the formation of non-stoichiometry compound of Na3Cl2 is confirmed by the diffraction, vibrational, spectroscopic and microscopic techniques. X-ray photoelectron spectroscopic study reveals the positive energy shift of Na 1 s peak which confirms the formation of higher coordination number Na3Cl2 (six to eight) such that it can be considered as Na rich structure. The typical cubic morphology has changed into butterfly wing structure under shocked conditions which is found to be novel, to date. Due to the formation of Na-rich crystal structure, the electrical properties of the shocked crystal are greatly altered. The maximum values of the real part of the impedance of the control and shocked crystals are 1.9 × 107 ohm and 1.0 × 107 ohm, respectively at the lower frequency regions. The present study offers a new platform to synthesize the stable non-stoichiometry NaCl structures under ambient conditions by low pressure acoustic shock waves which could bring about new understanding and implications on NaCl crystals and their applications.

The investigation of thickness-dependent mono-fractal, optical and optoelectronics properties of sputtered silver thin film for silicon solar cell

Here we report, the room temperature deposition of silver (Ag) thin films on silicon, glass and silicon solar cell substrates by magnetron sputtering. The effect of thickness on the deposited thin films and their morphological, fractal, optical and solar cell parameters have been extensively investigated. AFM results show that the Ag thin films are composed of different-size of nano-grains and the grain size increases with increasing thickness. Mono-fractal parameters, namely fractal dimension (Df) and Hurst exponent (H), were determined from the power spectral density function. X-ray photoelectron spectroscopy studies indicate that the deposited samples exhibit the presence of oxidation state of Ag (0) in thin films, confirming the stable structure. The optical analysis shows that the transmittance of the deposited thin films decreases with increasing thickness, on the other hand, the silver thin film with thickness of 20 nm shows surface Plasmon resonance (SPR) at 436 nm. Current-voltage (I–V) curves were measured in dark and under illumination mode at standard testing conditions, i.e., 300K, 1000 W/m2 and 1.5 AM global using a solar simulator. These measurement studies indicate that thicknesses are effectively impacts on photovoltaic performance. The calculated values of change in solar efficiency (Δη) are 0.26, −0.20, −0.76 and −6.88 % for thin films with nominal thickness 0.5, 1, 2 and 20 nm respectively.

Surface Chemistry of a [C2C1Im][OTf] (Sub)Wetting Layer on Pt(111): A Combined XPS, IRAS, and STM Study.

The concept of a solid catalyst with an ionic liquid layer (SCILL) is a promising approach to improve the selectivity of noble metal catalysts in heterogeneous reactions. In order to understand the origins of this selectivity control, we investigated the growth and thermal stability of ultrathin 1-ethyl-3-methylimidazolium trifluormethanesulfonate [C2C1Im][OTf] films on Pt(111) by infrared reflection absorption spectroscopy (IRAS) and X-ray photoelectron spectroscopy (XPS) in time-resolved and temperature-programmed experiments. We combined these spectroscopy experiments with scanning tunneling microscopy (STM) to obtain detailed insights into the orientation and adsorption geometry of the ions in the first IL layer. Furthermore, we propose a mechanism for the thermal evolution of [C2C1Im][OTf] on Pt(111). We observe an intact IL layer on the surface at temperatures below 200 K. Adsorbed [C2C1Im][OTf] forms islands, which are evenly distributed over the surface. The [OTf]- anion adsorbs via the SO3 group, with the molecular axis perpendicular to the surface. Anions and cations are arranged next to each other, alternating on the Pt(111) surface. Upon heating to 250 K, we observe changes in geometry and structural distribution. Whereas at low temperature, the ions are arranged alternately for electrostatic reasons, this driving force is no longer decisive at 250 K. Here, a phase separation of two different species is discernible in STM. We propose that this effect is due to a surface reaction, which changes the charge of the adsorbates. We assume that the IL starts to decompose at around 250 K, and thus, pristine IL and decomposition products coexist on the surface. Also, IRAS and XPS show indication of IL decomposition. Further heating leads to increased IL decomposition. The reaction products associated with the anions are volatile and leave the surface. In contrast, the cation fragments remain on the surface up to temperatures above 420 K.

Selective dissolution of micro-spherical Ca-Mn mixed oxides for efficient propane oxidation

The improvement of catalytic efficiency is of great significance to the removal of volatile organic compounds (VOCs), a class of key air pollutants leading to ground-level ozone pollution. Herein, a series of micro-spherical Ca-Mn mixed oxides (CaxMnyOz), namely CaMn3O6, Ca2Mn3O8 and CaMnO3, were prepared by a two-step precipitation method, and defects were constructed on which by selective dissolution to enhance the low-temperature catalytic performance in the oxidation of propane (C3H8) as a representative short-chain alkane VOCs. The synthesized CaxMnyOz oxides demonstrated drastically different response to the dissolution modification initiated by acid treatment. Specifically, after acid dissolution, while CaMn3O6 and Ca2Mn3O8 maintained largely their original structures, the perovskite-type CaMnO3 underwent lattice rearrangement and was transformed into γ-MnO2-like product with only a tiny amount of Ca. In C3H8 oxidation, the catalytic performance of CaMnO3 was significantly improved after selective dissolution, as indicated by a significant decrease of T90, i.e. the temperature to achieve 90% C3H8 conversion, from 455 °C to 240 °C. Mechanistic investigation by in-depth X-ray photoelectron spectroscopy studies revealed that selective dissolution led to higher Mn4+ concentrations and more oxygen vacancies on the oxide surfaces, thus facilitated electron transfer and O2 activation in C3H8 oxidation reactions. This study paves a new path for the design of cost-effective oxide catalysts toward the abatement of short-chain alkane VOCs.

Improving the Adhesion of Multi-Walled Carbon Nanotubes to Titanium by Irradiating the Interface with He+ Ions: Atomic Force Microscopy and X-ray Photoelectron Spectroscopy Study.

A complex study of the adhesion of multi-walled carbon nanotubes to a titanium surface, depending on the modes of irradiation with He+ ions of the "MWCNT/Ti" system, was conducted using atomic force microscopy and X-ray photoelectron spectroscopy. A quantitative assessment of the adhesion force at the interface, performed using atomic force microscopy, demonstrated its significant increase as a result of treatment of the "MWCNT/Ti" system with a beam of helium ions. The nature of the chemical bonding between multi-walled carbon nanotubes and the surface of the titanium substrate, which causes this increase in the adhesion of nanotubes to titanium as a result of ion irradiation, was investigated by X-ray photoelectron spectroscopy. It was established that this bonding is the result of the formation of chemical C-O-Ti bonds between titanium and carbon atoms with the participation of oxygen atoms of oxygen-containing functional groups, which are localized on defects in the nanotube walls formed during ion irradiation. It is significant that there are no signs of direct bonding between titanium and carbon atoms.