X-ray Photoelectron Spectroscopy Methods Research Articles

Gram-Scale Synthesis of CoO/C as Base for PtCo/C High-Performance Catalysts for the Oxygen Reduction Reaction

The composition, structure, catalytic activity in the ORR and stability of PtCo/C materials, obtained in two stages and compared with commercial Pt/C analogs, were studied. At the first stage of the synthesis performed by electrodeposition of cobalt on a carbon support, a CoOx/C composite containing 8% and 25 wt% cobalt oxide was successfully obtained. In the second step, PtCoOx/C catalysts of Pt1.56Co and Pt1.12Co composition containing 14 and 30 wt% Pt, respectively, were synthesized based on the previously obtained composites. According to the results of the composition and structure analysis of the obtained PtCoOx/C catalysts by X-ray diffraction (XRD), X-ray fluorescence analysis (XRF), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) methods, the formation of small bimetallic nanoparticles on the carbon support surface has been proved. The resulting catalysts demonstrated up to two times higher specific catalytic activity in the ORR and high stability compared to commercial Pt/C analogs.

New Palladium - ZrO2 Nano-Architectures from Thermal Transformation of UiO-66-NH2 for Carbonylative Suzuki and Hydrogenation Reactions.

The new nanocomposites, Pd/C/ZrO2 , PdO/ZrO2, and Pd/PdO/ZrO2 , were prepared by thermal conversion of Pd@UiO-66-Zr-NH2 (MOF) in nitrogen or air atmosphere. The presence of Pd nanoparticles, uniformly distributed on the ZrO2 or C/ZrO2 matrix, was evidenced by transmission electron microscopy, scanning electron microscopy (SEM), Raman and X-ray Photoelectron Spectroscopy (XPS) methods. All pyrolysed composites retained the shape of the MOF template. They catalyze carbonylative Suzuki coupling under 1 atm CO with an efficiency significantly higher than the original Pd@UiO-66-Zr-NH2 . The most active PdO/ZrO2 composite, formed benzophenone with TOF up to 1600 h-1 , while by using Pd@UiO-66-Zr-NH2 , much lower TOF values, 51-95 h-1 , were achieved. After the reaction, PdO/ZrO2 was recovered with the same composition and catalytic activity. Very good results were also obtained in the transfer hydrogenation of benzophenones to alcohols with Pd/C/ZrO2 and PdO/ZrO2 catalysts under microwave irradiation.

Role of Pt and PtO2 in the Oxygen-Evolution Reaction in the Presence of Iron under Alkaline Conditions.

The oxygen-evolution reaction (OER) through water oxidation is an inevitable reaction for water splitting toward storing energy. However, OER is a four-electron and slow reaction, which is also a bottleneck for water splitting. To find the role of Pt and PtO2 on the OER in the presence of Fe, the electrochemistry of Pt foil and PtO2 is investigated in the absence/presence of K2FeO4 as a soluble Fe salt at pH ≈ 13. After the addition of K2FeO4, a remarkable increase in the OER is recorded in the presence of Pt or PtO2. The obtained catalysts were characterized by operando visible spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy, electron-spin resonance spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and electrochemical methods. KOH solutions usually contain Fe and/or Ni impurities. It is found that neither Pt nor PtO2 is an OER catalyst in a Ni/Fe-free KOH, and even at an overpotential of 570 mV in purified KOH (pH ≈ 13), no clear OER was observed.

Cleaning high ash coal waste from coking coal via froth flotation method

In this work, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and laser particle size methods were employed. The surface of the particle obtained from the cyclonic-static microbubble flotation column (FCSMC) concentrate was coated with numerous small particles when compared to the clean coal collected from the Denver flotation cell. Even though the mass recovery of FCMSC concentrate (51.13%) was approximately twice the mass yield of Denver flotation cell concentrate (26.66%), the ash content in FCSMC concentrate (33.07%) was higher than that of the Denver flotation cell concentrate (14.88%). This result can be attributed to the advantages of FCSMC in small coal particle flotation, and this resulted in the misplacement of coarser particles with lower ash content in the tailing. The highest mass recovery of 0.250–0.500 mm in magnesium ion solution was 95.39%, which was slightly high than that (92.84%) in calcium ion solution. However, the concentrate ash content with 0.250–0.500 mm coarse size fraction in magnesium ion solution was 11.41%, which was higher than that (11.14%) in calcium ion solution. Flotation performances of different size fractions in rougher-cleaner flowsheet indicated that flotation responses in calcium ion solution were better than that in magnesium solution.

To reduce the passivation layer of Cu substrate by the ultrasonic assisted electrochemical potential activation method

In the micro electro mechanical system (MEMS) area, micro metal devices fabricating by the electroplating process were used widely in biology, medicine and optics field. However, due to the oxide layer of the metal substrate surface, the electroplating layer suffers from the poor adhesion. In order to reduce the oxide layer of the metal substrate surface, effects of the ultrasonic assisted electrochemical potential activation method have been investigated originally. The electrochemical test was processed by an electrochemical station. The oxide content of the substrate surface was measured by the X-ray photoelectron spectroscopy (XPS) method. The experimental results show that, comparing with the ultrasound free one, the ultrasonic assisted electrochemical potential activation method can improve the hydrogen evolution reaction and reduce the metal ion nucleation rate. Then the Cu substrate surface oxide content has been restored. Results of this paper can provide a new ultrasonic electrochemical potential activation method to activate the oxide layer of the substrate surface, as well as to improve the adhesion.

Study on the thermal conversion characteristics of demineralized coal char under pressurized O2/H2O atmosphere

The pressurized O2/H2O combustion technology can achieve nearly zero CO2 emissions during coal-fired power generation. In order to explore the influence of pressurized O2/H2O conditions on the thermal conversion characteristics of pulverized coal, Zhundong demineralized coal was used as raw material to prepare pyrolyzed char at 0.5 MPa and then the O2/H2O combustion experiments with different H2O concentration (0–40%), temperature (850-1000℃) and residence time (100–250 s) were carried out under the same pressure by a pressurized horizontal furnace. The carbon transformation, pore structure, carbon skeleton structure, and surface functional group structure of char under different experimental conditions were obtained by weighing method, Nitrogen adsorption test, Raman, and X-ray photoelectron spectroscopy methods, respectively. In addition, the reactivity of char was tested by thermogravimetric analyzer and micro fluidized bed reaction analyzer (MFBRA) to explore the relationship between the char structure and reactivity.

Aliovalent Doping of CeO2 Improves the Stability of Atomically Dispersed Pt.

Atomically dispersed supported catalysts hold considerable promise as catalytic materials. The ability to employ and stabilize them against aggregation in complex process environments remains a key challenge to the elusive goal of 100% atom utilization in catalysis. Herein, using a Gd-doped ceria support for atomically dispersed surface Pt atoms, we establish how the combined effects of aliovalent doping and oxygen vacancy generation provide dynamic mechanisms that serve to enhance the stability of supported single-atom configurations. Using correlated, in situ X-ray absorption, photoelectron, and vibrational spectroscopy methods for the analysis of samples on the two types of support (with and without Gd doping), we establish that the Pt atoms are located proximal to Gd dopants, forming a speciation that serves to enhance the thermal stability of Pt atoms against aggregation.

Chitosan functionalized gold-nickel bimetallic magnetic nanomachines for motion-based deoxyribonucleic acid recognition

In this present study, the preparation of chitosan functionalized gold‑nickel wire nanomachines (nanomotors) (CS@Au-Ni NMs) for motion-based double-stranded deoxyribonucleic acid (dsDNA) recognition and detection was described. Synthesis of the nanomachines was accomplished by Ni layer formation using direct current (DC) magnetron sputtering over electrochemically deposited Au wires. Subsequently, biopolymer chitosan was dispersed onto this bimetallic layer by drop casting which could provide a novel and functional surface for leading bio-applications. CS@Au-Ni NMs were characterized via scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and zeta potential analysis methods for the elucidation of structural morphology, elemental composition and electrophoretic mobility. On account of presenting the application of these magnetic nanomachines, they were interacted with different concentrations of dsDNA and the changes in their velocities were investigated. The speed CS@Au-Ni NMs were measured as 19 μm/s under 22 mT magnetic field. These magnetically guided nanomachines demonstrated a practical and good sensing ability by recognizing dsDNA between 0.01 mg/L and 10 mg/L. Electrochemical characterization was also performed to identify the surface characteristics. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments presented the interaction of the NMs with dsDNA by indicating the convenient recognition.

Synthesis of conical Co–Fe alloys structures obtained with crystal modifier in superimposed magnetic field

The addition of crystal modifier to electrolyte used during electrodeposition of metals and alloys allows obtaining conical structures without using any template. This method is fast and ensures covering large areas during one single electrodeposition process. In this work, Co–Fe cones were obtained by one-step method with ammonium chloride as a crystal modifier. The influence of electrodeposition parameters and electrolyte compositions were investigated. Electrodeposition conditions (duration, electrolyte temperature, and addition of NH4Cl), which allow obtaining the most uniform conical structures, were applied during sample fabrication in the magnetic field. The influence of its value and direction on the quality and compositions of obtained alloys was investigated using Scanning Electron Microscope (SEM) photos. To check if there is any change in the sample crystal system, the X-Ray Diffraction (XRD) analysis was performed. To confirm the synthesis of Co–Fe cones, they were analyzed using the X-ray photoelectron Spectroscopy (XPS) method.

STRUCTURAL FEATURES OF CHROMIUM CARBID COATINGS OBTAINED BY THE MOCVD METHOD FROM THE COL “BARKHOS”

Investigations of the structure and properties of gas-phase coatings obtained with the use of chromium organic liquid (COL) “Barkhos” have been carried out. The studies were carried out by the methods of nanoindentation, fractography, and X-ray photoelectron spectroscopy. It was found that such coatings have a two-level horizontallayered structure.

Corrosion evolution of Cu-Pb alloys from the Western Zhou Dynasty in simulated archaeological soil environment

• The corrosion behaviour of Cu-Pb alloy has been explained. • The Cu-13.28Pb alloy exhibited the best corrosion resistance. • The corrosion products are composed of metal oxides and metal-insoluble compounds. The corrosion behaviour study of Cu-Pb alloy in simulated archaeological soil environment were investigated using electrochemical accelerated corrosion, Field emission scanning electron microscopy/energy dispersive spectroscopy, laser scanning confocal microscope, X-ray photoelectron spectroscopy and electrochemical methods. It is crucial that the corrosion resistance of the Cu-Pb alloy was found to alter with the Pb content in the alloy. The results demonstrated that Cu-13.28Pb alloy exhibited the best corrosion resistance with the smallest corrosion current density and the lowest anodic dissolution rate. The corrosion products are mainly composed of matrix metal oxides and metal-insoluble inert compounds. The correlation between Pb content and corrosion behaviour and the corresponding corrosion mechanism were clarified.

Synthesis of a durable and efficient superhydrophobic copper mesh coated by organosilica nano/microstructures for separating oil from water

Superhydrophobic materials are widely utilized to separate oil from water. Proposing a facial method to synthesis a durable hydrophobic/superhydrophobic surface for efficient and easy oil/water separation is necessary due to the danger of oil spills for ecosystems. Herein, a robust superhydrophobic filter is introduced for oil/water separation. Organosilica nano/microstructures covered resorcinol-formaldehyde resin are loaded on the copper mesh surface to earn a roughened surface then modified by 1-dodecanethiol to get a low surface energy mesh. The prepared superhydrophobic copper mesh was shaped to a basket-like as an oil skimmer device that repels the water and collects the oil through its pores. The sample was analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy methods. The sample exhibits high water contact angle, θ=149±1° and the oil contact angle, showing its superhydrophobic nature. The prepared superhydrophobic mesh was used as an efficient and robust filter to separate oil from water. Its oil/water separation efficiency is more than 90% and this value approximately preserves after 50 cycles. The prepared sample also shows self-cleaning property. Thanks to the stable and rough structured created by resorcinol-formaldehyde resin covered by organosilica particles and also the low surface energy provided by 1-dodecanethiol, the prepared sample shows superhydrophobic property with high efficiency to separate oil from water.

Chemical degradation in Thermally Cycled Stainless Steel 316 with High-Temperature Phase Change Material

Analysis of stainless steel 316 as a containment material in the presence of a phase change material (PCM) cycled at high temperature was carried out through a combination of X-ray photoelectron spectroscopy and X-ray diffraction methods. In this work, stainless steel tokens were half-immersed in a chloride carbonate-based PCM, which were then thermally cycled in an air or a nitrogen environment up to 500 times, allowing the PCM to repeatedly transform between solid and liquid phases. Spectroscopy and diffraction methods were applied on the tokens, as well as the cycled PCM, to investigate the extent and nature of corrosion in such steel alloys. With varying sputtering conditions, the oxidation state at different depths of token surfaces was quantified. From the outermost corroded layer through to the bulk, this study shows a gradual change in distribution in both Cr and oxidation of Fe, while Cr was specifically found to have depleted and migrated into the PCM. The oxidation and depletion have been found to increase with increasing exposure time to PCM while sigma-phase structure embrittled in the corrosion layer. • Chemical degradation of thermal cycled SS 316 with PCM was analysed. • X-ray photoelectron spectroscopy methods were applied to analyse corrosion layers. • Chloride carbonate based PCM in air and nitrogen environment was studied. • With varying sputtering conditions, oxidation state of steel was quantified.

Preparation of WS2/C composite material and its electrocatalytic hydrogen evolution performance

With H2WO4 and EDA as precursors, WO3/C intermediate is obtained by mechanical stirring and in-situ solid-phase pyrolysis, then WS2/C composite material is obtained by high temperature vulcanization. The WS2/C composite is characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and other instrumental analysis methods. At the same time, the electrocatalytic performance of the catalyst was analyzed by the electrocatalytic steady-state polarization curve (LSV), Tafel slope (Tafel), cycle stability (CP), electrochemical impedance (PEIS) and Electrochemically Active Surface Area (ECSA) tests of the material. The results showed that when the current density of the WS2/C composite is 10 mA/cm2, overpotential is 179 mV, and Tafel slope is 98 mV/dec.

Laser-generated high entropy metallic glass nanoparticles as bifunctional electrocatalysts

High entropy metallic glass nanoparticles (HEMG NPs) are very promising materials for energy conversion due to the wide tuning possibilities of electrochemical potentials offered by their multimetallic character combined with an amorphous structure. Up until now, the generation of these HEMG NPs involved tedious synthesis procedures where the generated particles were only available on highly specialized supports, which limited their widespread use. Hence, more flexible synthetic approaches to obtain colloidal HEMG NPs for applications in energy conversion and storage are highly desirable. We utilized pulsed laser ablation of bulk high entropy alloy targets in acetonitrile to generate colloidal carbon-coated CrCoFeNiMn and CrCoFeNiMnMo HEMG NPs. An in-depth analysis of the structure and elemental distribution of the obtained nanoparticles down to single-particle levels using advanced transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) methods revealed amorphous quinary and senary alloy phases with slight manganese oxide/hydroxide surface segregation, which were stabilized within graphitic shells. Studies on the catalytic activity of the corresponding carbon-HEMG NPs during oxygen evolution and oxygen reduction reactions revealed an elevated activity upon the incorporation of moderate amounts of Mo into the amorphous alloy, probably due to the defect generation by atomic size mismatch. Furthermore, we demonstrate the superiority of these carbon-HEMG NPs over their crystalline analogies and highlight the suitability of these amorphous multi-elemental NPs in electrocatalytic energy conversion.

The Relationship between Cyclic Multi-Scale Self-Organized Processes and Wear-Induced Surface Phenomena under Severe Tribological Conditions Associated with Buildup Edge Formation

This paper presents experimental investigations of various interrelated multi-scale cyclic and temporal processes that occur on the frictional surface under severe tribological conditions during cutting with buildup edge formation. The results of the finite element modeling of the stress/temperature profiles on the friction surface are laid out. This study was performed on a multilayer coating with the top alumina ceramic layer deposited by CVD (chemical vapor deposition) on a WC/Co carbide substrate. A detailed analysis of the wear process was conducted by 3D wear evaluation, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and electron backscattered diffraction (EBSD), as well as X-ray photoelectron spectroscopy (XPS) methods. The following cyclic phenomena were observed on the surface of the tribo-system during the experiments: a repetitive formation and breakage of buildups (a self-organized critical process) and a periodical increase and decrease in the amount of thermal barrier tribo-films with a sapphire structure (which is a self-organization process). These two processes are interrelated with the accompanying progression of cratering, eventually resulting in the catastrophic failure of the entire tribo-system.

Electrochemically Obtained Polysulfonates Doped Poly(3,4-ethylenedioxythiophene) Films-Effects of the Dopant's Chain Flexibility and Molecular Weight Studied by Electrochemical, Microgravimetric and XPS Methods.

Electrochemically synthesized poly(3,4,-ethylenedioxythiophene) (PEDOT) films obtained in the presence of eight different polysulfonate dopants are comparatively studied by means of electrochemical quartz crystal microbalance (EQCM) and X-ray Photoelectron Spectroscopy (XPS). Differences with respect to oxidation and doping levels (OL and DL), polymerization efficiency and redox behavior are revealed based on the interplay of three factors: the type of the dopant (acid or salt form), flexibility of the polysulfonate chains and molecular weight of the polysulfonate species. For the rigid- and semi-rigid-chain dopants, use of the salt form results in higher OL and DL values and substantial involvement of solvent molecules in the course of polymerization and redox transitions whereas in the presence of their acid form compact PEDOT films with minor ionic-solvent fluxes upon redox transitions are formed. In contrast, use of the salt form of the flexible chain polysulfonates results in PEDOT with lower OL and DL in comparison to the corresponding acid form. Significant effects are observed when comparing flexible chain dopants with different molecular weights. From a practical point of view the present investigations demonstrate the large scope of possibilities to influence some basic properties of PEDOT (Ol and DL, intensity and type of the ionic and solvent fluxes upon redox transition) depending on the used polysulfonate dopants.

Electronic structure and stability of hexanuclear complex [Cu6(hfa)4(dpm)4(OH)4

Interatomic interactions and charge state of atoms in hexanuclear complex [Cu6(hfa)4(dpm)4(OH)4] have been studied by the methods of quantum chemistry and X-ray photoelectron spectroscopy (XPS). The shape and energy position of the Cu2p3/2-lines indicate that all copper atoms state could be interpreted as Cu2+. It was also analyzed the quantum chemical and XPS data on atomic charge distribution for monoligandic bis-β-diketonate Cu(hfa)2 and Cu(dpm)2 complexes. The comparison of calculated and experimental data for monoligandic and hexanuclear complexes revealed the electronic density redistribution on the oxygen and copper atoms in 1 due to the charge transfer interaction between Cu(hfa)2- and Cu(dpm)-fragments with participation of the bridging OH-groups, which was confirmed by NBO analysis.

Yolk-shell ZnO@C-CeO2 ternary heterostructures with conductive N-doped carbon mediated electron transfer for highly efficient water splitting

Herein, carbon-incorporated yolk-shell ZnO@C-CeO2 ternary heterostructures are employed as visible light responsive photocatalyst for highly efficient photoelectrochemical (PEC) water splitting. Compared to conventional ZnO/CeO2 semiconductors, introduction of a thin PDA shell layer assures the generation of a conductive N-doped graphitic carbon layer after a calcination post-treatment with mesoporous hollow morphologies. The evaluation of PEC water splitting performance of ZnO@C-CeO2 photoanodes reveals the maximum photocurrent density as 7.43 mA/cm2 at 1.18 V RHE under light whereas almost no response is recorded at dark. These superior PEC H2 evolution performance strongly implies efficient charge separation, facilitated charge transfer between photoanode and electrolyte interface as well as within the semiconductor bulk by means of rapid electron transfer ability of N-doped graphitic carbon layer and prolong life time of light inside yolk-shell structure. Furthermore, considerable depression in PL intensity of ZnO@C-CeO2 photoanodes compared to ZnO clearly reveals a higher photon absorption due to the reflection of light in hollow region and increase in electron hole separation efficiency. Moreover, plausible Z-scheme charge transfer mechanism using ZnO@C-CeO2 photoanodes under visible light illumination is verified using radical trapping experiments and X-ray photoelectron spectroscopy (XPS) methods, suggesting new generation of heterostructures for sufficient conversion of sunlight to H2 fuels.

Pd-loaded “Two-in-one” Covalent Organic Framework Composite Material: Synthesis, Characterization and Detection of Bisphenol A

We report a novel type of Pd-BFBAPy-COF (Pd-COF) loaded with Pd-NPs was synthesized for the first time by using “two-in-one” imine covalent organic framework materials as carrier. By using BFBAPy-COF (Py-COF) as the carrier and H2PdCl4 as the palladium source, Py-COF and Pd-NPs were combined by a simple heating and reflux method to successfully prepare Pd-COF. Through X-ray photoelectron spectroscopy (XPS) and other methods, it is proved that the loading of Pd-NPs on Pd-COF is completed by coordination. Finally, the application of Pd-COF as electrode coating material in the detection of Bisphenol A (BPA) by differential pulse voltammetry (DPV) shows that Pd-COF has a good electrochemical induction to BPA. This work provides a cheap and facile synthesis route for the preparation of an electrochemical detection material with practical value.