X-ray Photoelectron Spectroscopy Methods Research Articles

Detection of adsorbates on emissive MOF surfaces with X-ray photoelectron spectroscopy.

Luminescent metal-organic frameworks (MOFs) have been explored extensively as potential probes for nitroaromatic molecules, which are common constituents of explosive devices. Guest encapsulation within MOF pores is often cited as the prerequisite for emission changes, but the evidence for this signal transduction mechanism is often inadequate. Using the unique bipyridyl ligand AzoAEpP (2,2'-bis[N,N'-(4-pyridyl)ethyl]diaminoazobenzene), we constructed two luminescent pillared paddle-wheel Zn2+ MOFs using aryl dicarboxylate ligands 1,4-naphthalenedicarboxylic acid (ABMOF-1) and benzene 1,4-dicarboxylic acid (ABMOF-2). While both MOFs exhibit luminescence, 2,4-dinitrophenol only extinguishes ABMOF-1 emission. Since the size of the pores in ABMOF-1 precludes guest inclusion, we used X-ray photoelectron spectroscopy (XPS) to confirm the surface interaction and obtain insight into the nature of the quenching process. XPS experiments utilized a fluorinated nitroaromatic molecule, 4-trifluoromethyl-2,6-dinitrophenol, that extinguishes ABMOF-1 emission, and verified surface adsorption through a series of angle-resolved (ARXPS) and argon-ion sputter depth profile experiments. By further developing these techniques, we hope to develop a general approach for distinguishing between the various intermolecular interactions between MOFs and analytes that lead to changes in luminescence.

Electrochemical activity enhancement of monodisperse boron nitride quantum dots on graphene oxide: Its application for simultaneous detection of organophosphate pesticides in real samples

Organophosphate pesticides are toxic chemicals and not allowed in nearly all countries. It accumulates in water and soil owing to its low solubility and bioaccumulation causing serious health problems. A novel voltammetric sensor approach based on monodisperse boron nitride quantum dots (BNQDs) on graphene oxide (GO) was presented for simultaneous detection of organophosphate pesticides such as methyl parathion (MP), diazinon (DIA) and chlorpyrifos (CHL) in water samples. Scanning electron microscope (SEM), transmission electron microscope (TEM), x-ray diffraction (XRD) method, x-ray photo electron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods were used for all nanomaterials' characterizations. After that, BNQDs/GO composite modified glassy carbon electrode (BNQDs/GO/GCE) was prepared and 1.0 × 10−12–1.0 × 10−8 M was founded as the linearity range. The limit of detection (LOD) for MP, DIA and CHL was calculated to be 3.1 × 10−13 M, 6.7 × 10−14 M and 3.3 × 10−14 M, respectively. Finally, the prepared electrochemical sensor was used for water and apple juice samples analysis with high sensitivity and selectivity.

Structural study of amorphous and nanocrystalline Mg-based metallic glass examined by neutron diffraction, X-ray photoelectron spectroscopy, Reverse Monte Carlo calculations and high-resolution electron microscopy

The microstructure of amorphous and nanocrystalline Mg65Cu20Y10Zn5 alloy in as-quenched and post-annealed state was examined using neutron diffraction (ND), Reverse Monte Carlo modeling (RMC) and high-resolution transmission electron microscopy (HRTEM). The surface characteristic of Mg-based glass was investigated by X-ray photoelectron spectroscopy (XPS) method. The corrosion activity of alloy in glassy and nanocrystalline state was determined by electrochemical polarization measurements conducted in 3.5% NaCl solution. It was found that the structure of the melt-spun glass is homogeneous, but some medium-range order (MRO) regions as small as 1–2 nm were observed. The RMC analysis of ND data was used for local atomic structure and coordination numbers of the Mg65Cu20Y10Zn5 alloy in as-quenched state. The three-dimensional model representing a simulation box with atomic arrangements was also proposed. An average coordination number for Mg-Mg and Mg-Cu atoms is 8.1 and 2.5, adequately. The formation of nanocrystalline structure after annealing was confirmed by X-ray diffraction (XRD) and HRTEM observations. The TEM and HRTEM techniques allowed to observe regions containing very small particles in the amorphous matrix with size of 4–10 nm. The selected area electron diffraction (SAED) patterns allowed to identified hexagonal Mg and orthorhombic Mg2Cu phases. XPS results indicated the co-existence of MgO and Mg(OH)2 on the surface film formed on glassy ribbon in as-quenched state. The electrochemical polarization measurements revealed that the glassy ribbon exhibited lower corrosion current density than nanocrystalline sample.

XPS study of size effects of Fe3O4 nanoparticles on crosslinking degree of magnetic TFN membrane

The control of thin film nanocomposite (TFN) membranes cross-linking degree is an important factor to design new membranes and optimizing permeation characteristics. The Fe3O4 nanoparticle's based TFN membranes due to potentially added magnetic responsive properties to the membrane has a great importance in developing membrane architectures. Fe3O4/polyamide (PA) TFN membranes filled with nanoparticles in different sizes and concentrations have been synthesized. Cross-linking degree of PA layer characterized with Fourier transform spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) methods to evaluate size dependency of the cross-linking degree of PA layer network. Obvious correlations and competitions between concentration and size of nanoparticles which affect cross-linking degree have been developed. It has proven that with changing the size of the nanoparticles the concentration effects on polymerization and cross-linking can be tuned. Therefore optimization of size and concentration for fine tuning cross-linking degree in a proposed value is one of the consequences of this research. It concluded that size can be used as a powerful tool to design and engineer new and optimized membrane architectures.

Smartphone-assisted Colorimetric Analysis of Manganese in Steel Samples

Background: Manganese, Mn, is an essential element that is present in steels, and determines steel’s mechanical properties. Traditionally, atomic absorption and X-ray photoelectron spectroscopic methods were used for Mn analysis and complicated instrument operations, sometimes of high cost, are associated, and spectrophotometry/colorimetry is another tool for Mn analysis with simple operations. Nowadays, smartphone is emerging as a new powerful tool with multiple advantages in analytical chemistry. Objective: This project aimed to develop a simple and reliable smartphone-assisted colorimetric method to analyze Mn in steel samples. Method: Steel samples were first dissolved in the mixture of nitric acid and phosphoric acid to convert the elemental form of Mn into Mn(II) ions. The Mn(II) ions were then oxidized into the colored permanganate ions whose color was determined via a smartphone. Quantification of Mn was performed by comparing the unknown signal with the standard calibration curve which was constructed by plotting the green value of the solution as a function of the permanganate concentration with a 2nd polynomial regression fitting. The results from the developed method were then compared with the manufacturer values and another UV/vis spectrophotometry, using the Student t-tests, to validate the method. Results: The concentration of Mn in steel samples was determined by the smartphone-assisted colorimetry to be in the range of 0.56% to 0.97%, which had the same accuracy as the classic spectrophotometry and was in agreement with the manufacturer’s values. Conclusion: The experimental results proved that the smartphone-assisted method is a good alternative tool for Mn analysis in steels. Keywords: Smartphone, colorimetry, manganese, steel, permanganate, spectrophotometry.

Model Bimetallic Pd–Ag/HOPG Catalysts: An XPS and STM Study

A series of model bimetallic Pd–Ag catalysts with different ratios of metals and size distributions of supported particles was prepared by successive metal deposition onto a modified surface of highly oriented pyrolytic graphite (HOPG). X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were used to characterize the structural and electronic properties, as well as the morphology of nanoparticles at all stages of catalyst preparation. The use of the method made it possible to obtain bimetallic particles with various structures: alloyed, core–shell, and those consisting of individual monometallic particles. The XPS method with synchrotron radiation was used to determine the patterns in the formation of alloyed bimetallic particles, their chemical composition, structure, and the ranges of thermal stability under conditions of ultrahigh vacuum.

Preparation and electrochemical properties of Li0.33SrxLa0.56–2/3xTiO3-based solid-state ionic supercapacitor

A series of Sr2+-doped Li3×La2/3-x□1/3–2×TiO3 (LLT), i.e., Li0.33SrxLa0.56–2/3×□0.11–1/3×TiO3 (LSLT, □ represents vacancy), materials were synthesized and investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurement methods. Sr2+-doped LLT materials exhibited an increase in electrical conductivity when the doping content was ca. 0.25 mol% in our investigation. It was found that the doped elements were uniformly distributed, and no impurity phase was detected in the bulk materials. In addition, the improved electrical conductivity was probably caused by the proper enlargement of the Li+ migration path when Sr2+ ions, with a larger ionic radius, replaced La3+ ions and changed the Li+-La3+ bond after doping. The solid-state ionic supercapacitor, using-doped LSLT as an electrolyte, showed a capacitance of 0.48 mF g−1 for a 0.25 mol% Sr2+-doped sample.

Improving Functional Behavior of MCM‐41 by Encapsulating MnO 2 Nanorods towards Simultaneous Determination of Purine Bases in DNA Samples

MnO2 nanorods incorporated MCM-41 nanocomposite (MnO2@MCM-41) is synthesized and employed as an electrode modifier for individual as well as simultaneous detection of purine bases, guanine (GU) and adenine (AD). For this purpose MnO2 nanorods are encapsulated within MCM-41 by simple one pot synthetic approach. FT-IR, UV-vis absorption spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical methods are employed to characterize the nanocomposite and other materials. The electrochemical attributes of glassy carbon electrode (GCE) modified with the MnO2@MCM-41 (represented as GCE/MnO2@MCM-41) towards the determination of GU and AD is studied in detail. Upon incorporation of MnO2 nanorods on MCM-41, noticeable upsurge in anodic peak current with a decline in peak potential is observed for both GU and AD oxidations in cyclic voltammetry studies. Individual as well as simultaneous determination of GU and AD are performed using differential pulse voltammetry (DPV) technique which offered a linear range of 100 nM to 100 μM for GU and AD with respective limit of detections, 44 and 66 nM. The practical applicability of the GCE/MnO2@MCM-41 for real world samples analysis is satisfactorily demonstrated with certain DNA samples by DPV.

Formation and Study of Properties of Ta and Mo Nanocluster Films

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Formation of Surface Platinum Oxides in the Interaction of the Pt/Sibunit Catalysts with NO2: Estimates of the Width of Oxide Shell from XPS Data

The method of X-ray photoelectron spectroscopy (XPS) using two types of radiation, nonmonochromatic AlKα (hν = 1486.6 eV) and monochromatic AgLα (hν = 2984.3 eV), was used to study the interaction of the Pt/C (C = Sibunit) catalysts with NO2, which occurs in the preparation chamber of an XPS spectrometer at room temperature and NO2 pressure, equal to 3 × 10–6 mbar. It was found that, under these conditions, platinum was partially oxidized and metallic core becomes covered with a shell formed by a mixture of PtO and PtO2 oxides. The ratio of intensities Pt4f and Pt3d5/2 belonging to platinum oxides to the corresponding intensities of metallic platinum was used to estimate the width of oxide shell. For two of the three studied Pt/C samples, the width of the shell was 0.15–0.3 nm, which approximately corresponds to one monolayer of platinum oxide with a stoichiometry of PtO or PtO2.

Synthesis and electrochemical analysis of novel IrO2 nanoparticle catalysts supported on carbon nanotube for oxygen evolution reaction

In this paper, we report synthesis of novel nanoparticle catalyst of iridium oxide supported on carbon nanotube (IrO2/CNT) and characterization of activity and durability for oxygen evolution reaction (OER). The IrO2/CNT catalyst was prepared from iridium complex and COOH-CNT by hydrothermal method. The synthesized IrO2/CNT catalysts was characterized by transmission electron microscopy, x-ray diffraction, Raman microscopy, Fourier transfer-infrared spectroscopy, x-ray photoelectron spectroscopy, thermogravimetric analysis and electrochemical methods. The average particle size of the IrO2 particles on CNT is 1.7 nm and the loading amount of IrO2 is 4 wt%. The XPS measurement reveals that Ir complex was completely converted to iridium oxide through hydrothermal treatment. The IrO2/CNT catalyst showed sufficient performance for OER activity and durability in sulfuric acid solution. Our results indicate that IrO2/CNT is one of the prospective candidate catalysts for water electrolyzer.

Ternary MoS2/MoO3/C Nanosheets as High-Performance Anode Materials for Lithium-Ion Batteries

Ternary MoS2/MoO3/C nanosheets were successfully synthesized via a chemical vapor deposition method. The hybrids were characterized by x-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy, raman and x-ray photoelectron spectroscopic methods. The as-obtained MoS2/MoO3/C nanosheets applied as an anode material for lithium-ion batteries, showed high initial discharge/charge capacities at current rates of 0.5C, 1640.9 mA h g−1 and 1393.8 mA h g−1 respectively, with initial coulombic efficiency of approximately 84.9%. The material exhibited superior rate capabilities, with specific discharge capacities of 1240.2 mA h g−1, 1048.5 mA h g−1, 917.2 mA h g−1, 742.3 mA h g−1, 663.6 mA h g−1, 601.8 mA h g−1 and 593.4 mA h g−1 at current rates of 0.2C, 0.4C, 1C, 4C, 8C, 12C and 15C, respectively. This superior electrochemical performance was mainly due to the uniformly-distributed MoS2 nanosheets and to highly graphitized carbon, which not only mitigated mechanical stress during repeated cycling, but also provided good conductivity.

Analysis of the Thermal Stability of Very Thin Surface Layers of Corrosion Inhibitors by Time-of-Flight Secondary Ion Mass Spectrometry.

The powerful nature of the secondary ion mass spectrometry (SIMS) technique was explored in order to analyse very thin surface layers that were self-assembled on steel material from acidic solution. These surface layers are adsorbed corrosion inhibitors. The SIMS technique proved useful to characterise the molecular structure and homogeneity of thin surface layers in the nanometre range of specific analytes on the metallic substrate. Using SIMS, the thermal stability of these layers was further investigated and the desorption energy at a certain temperature was determined, where special attention was devoted to the method's static limit. In order to compare, and for certain cases emphasise, the benefits gained by using SIMS in such surface analysis compared with the X-ray photoelectron spectroscopy (XPS) method, the same samples were also analysed by means of the latter. XPS is usually considered to be the most powerful analytical tool in surface analysis studies, but, as shown herein, it has certain limitations compared to SIMS. Finally, the surface topography was investigated by employing atomic force microscopy (AFM) in order to carry out a comprehensive surface analysis. Graphical Abstract ᅟ.

An effect of electrode material on pinning layer characteristics and depolarization field in polymer ferroelectrics

An effect of electrode materials on the process of oriented film polarization of ferroelectric copolymers of vinylidenefluoride and tetrafuoroethylene has been studied. Electrodes of Al and Au were used, with their work function values being substantially different. Polarization was carried out by high-voltage impulse supply from which remnant polarization was estimated. Under the same conditions, the latter was shown to be higher in films with Au electrodes. The cause of this phenomenon was studied by the method of X-ray photoelectron spectroscopy, when chemical changes in the polymer surface were observed in situ during metal deposition on it. It was found that when Al was deposited, new functional groups were formed on the polymer surface. It was assumed that unlike in the case of Au, there was no complete compensation of the ferroelectric field, and the local field turned out to be lower than that determined by the external source.

Nitrogen and Sulfur Co-Doped MWCNT/Rgo Composite As Highly Active Electrocatalyst for Oxygen Reduction Reaction in Alkaline Fuel Cell

Recently a major effort in fuel cell research and development have been undertaken to displace platinum with platinum-free or even better, totally metal free catalyst materials. With the possibility of using heteroatom doped carbon-based materials as electrocatalysts for oxygen reduction reaction (ORR) instead of Pt, anion exchange membrane fuel cells (AEMFCs) have big advantage over other low-temperature fuel cells. Beside other carbon nanomaterials, carbon nanotubes and graphene have shown good electrocatalytic and catalyst supporting properties for different fuel cell cathode catalysts. Graphene and/or carbon nanotubtube doping with heteroatoms is a common strategy to increase the electrocatalytic activity of these materials towards the ORR [1]. Different heteroatoms, such as nitrogen, phosphorous, sulfur and boron have been studied as promising dopants to prepare electrocatalysts for ORR in alkaline media [2]. In this work the electrocatalytic activity of nitrogen and sulfur co-doped MWCNT/rGO was studied towards the ORR in alkaline media (0.1 M KOH) using the rotating disc electrode (RDE) method. The catalyst materials were prepared by doping of MWCNT/rGO with N and S via simple one-pot synthesis method using high-temperature pyrolysis in inert gas atmosphere. The resulting catalyst material exhibited excellent electrocatalytic activity towards the ORR in alkaline media. Catalyst samples were characterized also by transmission electron microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy methods. Fuel cell experiments were carried out using Fumatech Fumapem® FAA anion-exchange membrane and FAA ionomer. Methanol tolerance and long-term stability tests were performed. The results revealed remarkable catalytic activity of nitrogen and sulfur co-doped carbon towards the ORR in alkaline media, as well good methanol tolerance. Composition analysis with different physical characterization methods confirmed that nitrogen and sulfur have been grafted onto the carbon support. RDE tests demonstrated highly improved catalytic activity in comparison with undoped MWCNT/rGO and fuel cell tests showed a great potential of N and S doped carbon as alternative cathode catalyst and catalyst carrier for anion exchange membrane fuel cells.

Modification of polyethylene tube surface in dielectric barrier discharge

Abstract

X-ray photoelectron spectroscopy study of the interaction of lithium with graphene

Abstract Graphene-like nanostructures, solely or in combination with redox active compounds, are an important component of battery electrodes. Design of effective electrode materials requires a deep understanding of electrochemical reactions occurring at graphene surfaces. The methods of X-ray photoelectron spectroscopy (XPS) are very helpful in such research, providing the composition of studied samples and electronic state of individual elements. In this chapter, we demonstrate advantages of XPS for monitoring of chemical vapor deposition graphene growth and lithium penetration under graphene layers, disclosing of interactions with metals and interface states.

Intensification of Eudialyte Concentrate Leaching by Nanosecond High-Voltage Pulses

The mechanism of weakening and directional change in structural and chemical properties of eudialyte under nonthermal exposure to nanosecond high-voltage electromagnetic pulses and nitric-acid leaching is studied. The methods of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy and microhardness measurement are used. The rational mode of high-energy pulsed treatment is determined. After such mode treatment, the acid leaching of eudialyte concentrate results in recovery of zirconium and total rare earth elements higher by 1.7 and 1.4 times as against reference standards.

Preparation of N-doped graphene-based electrode via electrochemical method and its application in vanadium redox flow battery

An N-doped graphene electrode has been prepared by cyclic voltammetric method in 5.0 M of HNO3 solution on a graphite-based electrode at room temperature. The modification of the electrode surface with different types of N-containing groups, such as nitro groups, pyrrolic N, and pyridinic N, has been controlled by changing the scanned potential ranges. The formation of an N-doped graphene electrode has been confirmed by scanning electron microscopic, atomic force microscopic, X-ray photoelectron, and Raman spectroscopic methods. The prepared N-doped graphene-modified electrodes have been used in positive electrolyte of a vanadium-based redox flow battery. As positive electrodes, the electrochemically modified electrodes prepared in 5.0 M of HNO3 solution −1.0 to (+1.9) and −0.7 to (+1.9) V had more than 140 and 120 mA/cm2 anodic and cathodic peak currents, respectively, in vanadium redox battery. This fast, low-cost, and environmentally friendly method can be used in many application areas, such as optical devices, (bio)sensors, energy storage materials, and electronic devices.

Short-Range Order and Charge Transport in SiOx: Experiment and Numerical Simulation

The structure of nonstoichiometric silicon oxide (SiOx) has been studied by the methods of highresolution X-ray photoelectron spectroscopy and fundamental optical-absorption spectroscopy. The conductivity of SiOx (x = 1.4 and 1.6) films has been measured in a wide range of electric fields and temperatures. Experimental data are described in terms of the proposed SiOx structure model based on the concept of fluctuating chemical composition leading to nanoscale fluctuations in the electric potential. The maximum amplitude of potential fluctuations amounts to 2.6 eV for electrons and 3.8 eV for holes. In the framework of this model, the observed conductivity of SiOx is described by the Shklovskii–Efros theory of percolation in inhomogeneous media. The characteristic spatial scale of potential fluctuations in SiOx films is about 3 nm. The electron-percolation energy in SiO1.4 and SiO1.6 films is estimated to be 0.5 and 0.8 eV, respectively.