X-ray Photoelectron Spectroscopy Experiments Research Articles

In situ photoelectron spectroscopy for characterizing the chemical evolution of a carbon steel surface by heat-treatment

The microstructure that governs the nature of carbon steel is determined by the combination of iron and carbon. Ferrite and austenite differ in their arrangements of iron atoms, and they differ from cementite with respect to iron and carbon bonding. In this work, we combine structural studies (X-ray diffraction, scanning electron microscopy, and atomic force microscopy) and synchrotron-based in-situ X-ray photoelectron spectroscopy (XPS) to demonstrate the behavior of the carbon in carbon steel using a thermal annealing process conducted from room temperature to 900 °C in an ultrahigh-vacuum chamber. In situ XPS experiments revealed not only that the chemical states varied depending on depth from the surface but also that the carbide changed into the C-solute phase at temperatures between than 300–600 °C. Our findings provide important insights into the subtle balance of interactions involving the properties of steel that differ between the surface and bulk phases, offering new opportunities to engineer the properties of carbon steel.

Bimetallic synergy boost TCPP(Ni)-Co MOF as the high-performance electrochemical sensor for enhanced detection of trace theophylline

A bimetallic porphyrin MOF TCPP(Ni)-Co has been synthesized by the combination of reflux method and hydrothermal method. Due to the inherent conjugated ligand TCPP and the synergistic effect between metal center Co2+ and Ni2+, the TCPP(Ni)-Co MOF could work as the high-performance electrochemical sensor by the modification on the GCE. TCPP(Ni)-Co@GCE could realize the detection of trace theophylline with high sensitivity, fast response time (less than 3 s), detection range of 10–100 nM, and the extreme detection limit as low as about 3.3 nM. The good stability, repeatability and anti-interference performance further support TCPP(Ni)-Co MOF function as an excellent electrochemical sensor for theophylline. The enhanced detection mechanisms have been carefully discussed with X-ray photoelectron spectroscopy (XPS) and cyclic voltammograms (CVs) experiments. The coordination of Ni2+ in higher electron affinity could construct more electron-deficient environment in the well conjugate TCPP ligand, which could reduce the electron compensation to Co2+ in the formation of Co-COO coordination bond and set “Co-COO” in a higher oxidation state, thus enables TCPP(Ni)-Co MOF as the high-performance sensor for trace theophylline.

Electrochemically controlled solid liquid interfaces probed with lab-based X-ray photoelectron spectroscopy

A micro-electrochemical cell is sealed with 2–5 layers of graphene to monitor the changing oxidation state of Cu nanoparticles (NPs) with X-ray photoelectron spectroscopy (XPS) in a mildly alkaline aqueous solution under electrochemical control. The main role of graphene is to ensure an abrupt change between the liquid and vacuum environments, where the latter is required for conducting XPS experiments. Decent transparency to the generated photoelectrons with a kinetic energy of few hundred eV is another requirement that graphene fulfils for performing such experiments. Graphene also acts as an electrically conducting support material for Cu NPs, ensuring that a bias can be applied to them. The proof-of-concept measurements presented in this work show that relatively lower flux X-ray sources, such as those with Al-Kα emission that are commonly used in laboratories, are sufficient for probing the solid–liquid interfaces with this approach.

Enhanced coalbed methane recovery by the modification of coal reservoir under the supercritical CO2 extraction and anaerobic digestion

Coal reservoir is considered as the ideal site for coalbed methane (CBM) occurrence, biomethanation and CO2 sequestration. Four coal samples with different ranks were selected to conduct supercritical CO2 (Sc-CO2) extraction and anaerobic digestion (AD). X-ray photoelectron spectroscopy, mercury intrusion, and isothermal adsorption experiments were performed on the raw coal samples and the remaining coal samples after Sc-CO2 and Sc–CO2–AD to analyze the mechanism of enhanced CBM recovery by reservoir modification. The results showed that coal pore volume and porosity are greatly increased after Sc-CO2 extraction. Meanwhile, the reduction of the oxygen-containing functional groups and the micropore specific surface area determined the weakening of the adsorption capacity of coal. After Sc–CO2–AD, the macropore volume and porosity of coal continued to increase, and the permeability of coal was effectively improved. And the oxygen-containing functional groups and micropore specific surface area continued to decrease, which determined that the adsorption capacity of coal for methane continued to decrease. Sc-CO2 and AD can mutually promote the modification of coal reservoirs. These effects are quite favorable for gas desorption, migration and production during CBM exploitation, which provide powerful supports for CO2 emission reduction, CO2 geological sequestration and CBM production enhancement.

Influence of support textural property on CO2 to methane activity of Ni/SiO2 catalysts

In this work, we elucidated the role of physicochemical textural properties of inert support on the catalyst activity by impregnating Ni on ordered mesoporous silica (SBA-15 and MCM-41) and non-mesoporous silica (nMPS). The catalyst Ni/SBA-15 exhibited the best CO2 conversion (83%) and product selectivity (99.9 %) followed by Ni/MCM-41 and the least by Ni/nMPS. The difference in the nature of the catalyst, degree of nanoparticle distribution and nanoparticle encapsulation by different silica support were studied by N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS) experiments. The Operando Diffused Reflectance Infrared Fourier Transform Spectroscopy were used to understand the variance in reaction pathway which is accredited to the textural properties of the support. The SBA-15 supported Ni catalyst followed dissociative CO pathway while MCM-41 and nMPS reacted through associative formate mechanism as major pathway. These findings provide a novel perspective on CO2 hydrogenation over Ni-silica, allowing us to tune both activity and selectivity.

High dielectric permittivity and ultralow dielectric loss in Nb-doped SrTiO3 ceramics

In this study, we prepared a series of Nb-doped SrTiO3 ceramics sintered in both air and N2 atmospheres. The X-ray diffraction (XRD) analysis indicated that all samples had a pure cubic phase perovskite structure with no secondary phase. The dielectric test showed that the Nb-doped SrTiO3 ceramics had a high dielectric permittivity (>3 × 104) and low dielectric loss (<0.004) over a broad temperature range from −100 to 300 °C with a breakdown strength over 20 kV/cm. The dielectric performance is attributed to the designated TiTi′−VO··−TiTi′ deep-lattice-defect states localising weak-hopping electrons to generate high defect-dipole concentrations, as verified by systematic X-ray photoelectron spectroscopy (XPS) experiments. This study offers a route for designing other types of high dielectric permittivity ceramics.

Hg0 Removal by a Palygorskite and Fly Ash Supported MnO2-CeO2 Catalyst at Low Temperature

MnO2-CeO2/PG-FA catalysts were prepared by supporting MnO2-CeO2 to PG-FA and used to remove Hg0 in simulated flue gas. The results show that MnO2-CeO2/PG-FA catalyst had excellent and stable Hg0 removal activity, which was mainly due to the combination effect of the catalytic oxidation activity by MnO2-CeO2 and the adsorption ability by PG-FA. Mn8-Ce0.5/PG-FA (with 8.0% MnO2 and 0.5% CeO2 loading) catalyst showed the highest Hg0 removal efficiency at 140 °C and Hg0 removal efficiency could be maintained above 95% with the space velocity of 6000 h−1 and Hg0 concentration of 160 μg/m3. O2 promoted Hg0 removal by MnO2-CeO2/PG-FA catalyst, while SO2 and H2O had inhibitory effects. In the presence of O2, the inhibitory effect of SO2 and H2O can be obviously weakened. MnO2-CeO2/PG-FA catalysts were characterized with scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption experiments (TPD). The results of SEM and XRD showed that the active components MnO2-CeO2 dispersed well on the surface of PG-FA support. The results of XPS and TPD show that the Hg0 removal process over MnO2-CeO2/PG-FA catalyst included adsorption and oxidation, HgO and HgSO4 were generated and adsorbed on the catalyst. MnO2-CeO2/PG-FA catalyst also showed excellent regeneration performance after Hg0 removal.

Experimental and Computational Studies on Octyl Hydroxamic Acid as an Environmentally Friendly Inhibitor of Cobalt Chemical Mechanical Polishing.

Octyl hydroxamic acid (OHA) was investigated as an inhibitor in H2O2-based alkaline silica dispersions for the polishing of cobalt (Co) films for interconnect applications. A combination of experiments and density functional theory (DFT) was used to investigate the inhibition effect and the mechanism of OHA on the Co surface. On the basis of the experiments, it can be proven that OHA has an inhibition effect on Co, which came from the inhibition of the cathodic reaction. The X-ray photoelectron spectroscopy (XPS) experiments show that the adsorption of OHA weakened the oxidation of the Co surface and protected the Co surface from corrosion. On the basis of the calculations, it can be proven that the OHAketone (ion) is most likely to react with the Co surface, and it can adsorb on the Co surface by Co-O bonds. This study provides important microscopic insights for understanding the corrosion protection of Co interconnect metals and helps to explain the corrosion inhibition mechanism of the organic-metal interface during the CMP process.

Lithium-induced intralayer rearrangement of molybdenum disulfide: Effect of graphene coating

Nanoscale composites consisting of molybdenum disulfide and graphene (MoS2/graphene) are promising anode materials for lithium-ion batteries. In this work, to gain insight into the role of graphene coating in the interaction of lithium with MoS2, we used in situ X-ray photoelectron spectroscopy (XPS) experiments. The deposition of lithium was carried out in a high vacuum simultaneously on the surface of polycrystalline MoS2 and MoS2 coated with a few-layer graphene. The XPS Mo 3d and S 2p spectra of lithiated samples exhibited the appearance of low-energy components assigned to MoMo bonds and weakened S–Mo bonds according to the density functional theory calculations. Such an atomic rearrangement in the MoS2 layer was much more significant for MoS2/graphene due to excess lithium in the interface. Annealing of the samples at 500 °C revealed that the lithium-induced intralayer MoS2 rearrangement is irreversible despite the removal of lithium. Moreover, at 800 °C, the rearranged MoS2 regions containing the residual lithium decomposed to form metallic molybdenum and Li2S2. This finding can help to understand the processes occurring in MoS2/graphene electrodes and to develop advanced materials for efficient lithium-ion batteries.

Nitrogenous gas formation mechanisms of chemically modified superfine pulverized coal during pyrolysis

ABSTRACT The pyrolysis products are affected by the O-containing groups in coal. The influences of the introduced O-containing groups on nitrogenous gas formation are rarely explored. To investigate this issue, superfine pulverized coal samples were modified by several kinds of selected chemical reagents. 13C nuclear magnetic resonance spectroscopy (NMR) experiments demonstrate that a considerable amount of carboxyl, hydroxyl structures is introduced into the carbon skeleton after peracetic acid modifications. X-ray photoelectron spectroscopy (XPS) experiments reveal that the content of quaternary nitrogen N-Q on the surface of the samples modified by peracetic acid remain unchanged in general. And oxidized nitrogen N-X structures are formed by the oxidation of pyridinic nitrogen N-6 and pyrrolic nitrogen N-5, which induces the proportion of N-X to increase more than 40%. Because of the introduction of O-containing functional groups, the discrepancy of nitrogenous gas composition has been found between the raw and modified samples during pyrolysis. The production of N2O soars between 200°C and 300°C. After H2O2 modifications, the formation paths of nitrogenous gas do not change significantly due to the absence of O-containing group introduction. This research uncovers that the introduced O-containing groups alter the formation paths of nitrogenous gas in coal during pyrolysis and elucidates the mechanism.

Metal-Free Chemoselective Reduction of Nitroarenes Catalyzed by Covalent Triazine Frameworks: The Role of Embedded Heteroatoms.

Chemoselective reduction of nitroarenes to arylamines is a core technology for the synthesis of numerous chemicals. The technology, however, relies on applying precious noble metal catalysts. We present our findings on the development of robust nanoporous covalent triazine frameworks (CTFs) as metal-free catalysts for the green chemoselective reduction of nitroarenes. The turnover frequency is found to be 43.03 h-1, exceeding activities of the heteroatom-doped carbon nanomaterials by a factor of 30. The X-ray photoelectron spectroscopy and control experiments provide further insights into the nature of active species for prompt catalysis. This report confirms the importance of quaternary 'N' and 'F' atom functionalities to create active hydrogen species via charge delocalization as a critical step in improving the catalytic activity.

A comparative study of activation of peroxymonosulfate and peroxydisulfate by greigite (Fe3S4) for the degradation of sulfamethazine in water

In this study, greigite (Fe3S4) was used to activate peroxymonosulfate (PMS) and peroxydisulfate (PDS) for sulfamethoazine (SMT) degradation in water. The possible influencing factors such as oxidant concentration, sulfur sources, iron sources and initial pH were investigated.Experimental results showed that SMT could be completely removed at 0.1 mM PMS in 15 min in Fe3S4/PMS system. 96.7% of SMT was removed at 1.0 mM PDS in 60 min in Fe3S4/PDS system.Both systems had good performance over a wide pH range of 3–9. In addition, different sulfur sources could affect the crystal structure, morphology and composition of the synthesized catalysts, while different iron sources had little influence. Quenching experiments and electron paramagnetic resonance (EPR) test evidenced that the activation of PMS and PDS by Fe3S4 was a multi-reactive oxygen species process with the coexistence of •OH, SO4•−, O2•− and 1O2. SO4•− was the main active species in the Fe3S4/PMS system, while SO4•− and •OH were the main free radicals in the Fe3S4/PDS system. X-ray photoelectron spectroscopy (XPS) experiments showed that Fe(II) on Fe3S4 surface effectively activated PMS and PDS, and S2− species were key factors controlling Fe(II) regeneration and subsequent activation of PMS and PDS.However, the consumption of Fe(II) and S2− in Fe3S4/PDS system was higher than that in Fe3S4/PMS system. In addition, in the two systems, the degradation intermediates of SMT and their practical application were also evaluated.This study provided a systematic evaluation of the performance of Fe3S4/PMS and Fe3S4/PDS systems for treatment of antibiotic contaminated water.

Sintering behavior, structure, and microwave properties of novel Li2xCu1-xMoO4 ceramics

In this study, we prepared a novel series of Li2xCu1-xMoO4 (x = 0.02, 0.04, 0.06, 0.08, and 0.10) microwave ceramics. The dynamic sintering behavior, crystal phases, micro-morphologies, and dielectric properties of the samples were studied. The substitution of Li+ contributed to refining the crystal grain size, promoting the densification of microstructure, and enhancing the quality factor. Due to different valence substitutions, Cu+ ions were created, which were verified by X-ray photoelectron spectroscopy (XPS) and Raman experiments. In addition, the Raman shift, full width at half maximum (FWHM) value of the A1g peak, and crystal microstrains were analyzed to gain a mechanistic understanding of the influence of structure on the dielectric properties. When x = 0.08, the Li2xCu1-xMoO4 ceramic sintered at 675 °C exhibited optimal comprehensive properties with εr = 8.17, Qf = 68 476 GHz, and τf = −25 ppm/°C, and good chemical stability between the ceramic and Al electrode was also achieved. These promising properties make Li2xCu1-xMoO4 (x = 0.08) more suitable for ultra-low temperature co-fired ceramic (ULTCC) applications.

Electrochemical and X-ray Photoelectron Spectroscopy Surface Characterization of Interchain-Driven Self-Assembled Monolayer (SAM) Reorganization.

Herein, we report a combined strategy encompassing electrochemical and X-ray photoelectron spectroscopy (XPS) experiments to investigate self-assembled monolayer (SAM) conformational reorganization onto an electrode surface due to the application of an electrical field. In particular, 3-mercaptopriopionic acid SAM (3MPA SAM) modified gold electrodes are activated with a 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysulfosuccinimide (NHSS) (EDC-NHSS) mixture by shortening the activation time, from 2 h to 15/20 min, labelled as Protocol-A, -B and -C, respectively. This step, later followed by a deactivation process with ethanolamine (EA), plays a key role in the reaction yields (formation of N-(2-hydroxyethyl)-3-mercaptopropanamide, NMPA) but also in the conformational rearrangement observed during the application of the electrical field. This study aims at explaining the high performance (i.e., single-molecule detection at a large electrode interface) of bioelectronic devices, where the 3MPA-based SAM structure is pivotal in achieving extremely high sensing performance levels due to its interchain interaction. Cyclic voltammetry (CV) experiments performed in K4Fe(CN)6:K3Fe(CN)6 for 3MPA SAMs that are activated/deactivated show similar trends of anodic peak current (IA) over time, mainly related to the presence of interchain hydrogen bonds, driving the conformational rearrangements (tightening of SAMs structure) while applying an electrical field. In addition, XPS analysis allows correlation of the deactivation yield with electrochemical data (conformational rearrangements), identifying the best protocol in terms of high reaction yield, mainly related to the shorter reaction time, and not triggering any side reactions. Finally, Protocol-C’s SAM surface coverage, determined by CV in H2SO4 and differential pulse voltammetry (DPV) in NaOH, was 1.29 * 1013 molecules cm−2, being similar to the bioreceptor surface coverage in single-molecule detection at a large electrode interface.

Evolution of pore characteristics and methane adsorption characteristics of Nanshan 1/3 coking coal under different stresses

To ascertain the evolution of pore characteristics and methane adsorption characteristics of the unit cell of Nanshan 1/3 coking coal under different stresses, proximate analysis, ultimate analysis, solid-state 13C nuclear magnetic resonance spectroscopy (13C-NMR) and X-ray photoelectron spectroscopy (XPS) experiments were performed on the coal samples, and a molecular unit cell model of 1/3 coking coal was established. As the increase of stress, pore diameter, proportion of larger pores, number of pores, surface area, and pore volume all decrease, the rate of decrease gradually decreases, and the smaller pores are less affected. Under 8 kinds of stress, the methane adsorption capacity and the overall system energies all conform to the Langmuir adsorption curve; as the stress increases, the methane adsorption capacity and the overall system energies both decrease, the rate of decrease gradually decreases, and the order of the adsorbed methane increases. Stress changes the methane adsorption capacity by changing the pore characteristics of the unit cell, and the stress has a more obvious effect on larger pores. As the stress increases, the speed of the stress's influence on the pores weakens. This has certain guiding significance for studying the saturated adsorption capacity of methane under different original in-situ stresses.

Simultaneous immobilization of arsenic, lead and cadmium by magnesium-aluminum modified biochar in mining soil

Owing to the human activities such as smelting and mining, arsenic (As), lead (Pb) and cadmium (Cd) seriously polluted the soil of non-ferrous metal mining areas, thus efficient methods for the simultaneous immobilization of the three heavy metals are urgently needed. In the present study, Mg–Al modified biochars (MABs) were synthesized through a simple one-pot pyrolysis method to immobilize the three heavy metals. According to the BET (Brunauer-Emmett-Teller) test method, MABs had larger specific surface areas than biochar. Compared to the materials obtained at 300 °C and 700 °C, MAB with a pyrolysis temperature of 500 °C (MAB 500) had a significant immobilization effect on As, Pb and Cd in the Gansu mining area. Compared with BC, the removal efficiencies of As, Pb and Cd increased from −62%, 17% and 5% to 52%, 100% and 66%, respectively. And the toxicity characteristic leaching procedure (TCLP) test showed that the leaching concentrations of the three heavy metals in the treated soil were all lower than the standard value. X-ray photoelectron spectroscopy and kinetic experiments showed that there were various mechanisms in the immobilization process of the three heavy metals, and the large specific surface area and the multi-Mg/Al–OH of MABs play an important role in this process. More charges were provided by larger specific surface for ion exchange with heavy metals. In addition, larger specific surface area also provided more adsorption sites. More complex sites were provided by Mg/Al–OH to form Mg/Al–O-M then immobilize the heavy metals. In summary, the immobilization mechanism may involve electrostatic attraction, precipitation/co-precipitation, and surface complexation.

Strain-Assisted Single Pt Sites on High-Curvature MoS 2 Surface for Ultrasensitive H 2 S Sensing

Strain-Assisted Single Pt Sites on High-Curvature MoS ₂ Surface for Ultrasensitive H ₂ S Sensing

Ppm-level Cu dopant on ultrathin Pd nanosheets/TiO2 for highly enhanced photocatalytic alcoholysis of epoxides

Photocatalysis provides a new avenue for organic synthesis, to which catalyst design at atomic level holds the key. Herein, the first case of ppm-level (39 ppm) Cu dopant based photocatalyst has been successfully constructed as Cu1Pd200/TiO2, in which Cu element dopes ultrathin Pd nanosheets (thickness of 2 nm) with atomic dispersion using TiO2 as the semiconductor host. The alcoholysis of styrene oxide, as a model reaction, can produce valuable β-alkoxy alcohols, conventionally requiring corrosive strong acids or harsh reaction conditions. The presence of ppm-level Cu atoms in Cu1Pd200/TiO2 can boost alcoholysis with a quite high reaction rate of 176 mmol·g−1·h−1 at room temperature under light illumination (100 mW·cm2), which is 6 times and 17 times higher than Pd/TiO2 and bare TiO2, respectively. Moreover, the Cu-doped photocatalyst presents excellent stability without deactivation after ten cycles. Based on X-ray photoelectron spectroscopy, infrared spectroscopy and control experiments, this unexpected photocatalytic behavior mainly origins from the electron transfer effect and unique chemisorption of epoxides owing to Cu dopant.

Role of the voltage window on the capacity retention of P2-Na2/3[Fe1/2Mn1/2]O2 cathode material for rechargeable sodium-ion batteries

P2-Na2/3[Fe1/2Mn1/2]O2 layered oxide is a promising high energy density cathode material for sodium-ion batteries. However, one of its drawbacks is the poor long-term stability in the operating voltage window of 1.5–4.25 V vs Na+/Na that prevents its commercialization. In this work, additional light is shed on the origin of capacity fading, which has been analyzed using a combination of experimental techniques and theoretical methods. Electrochemical impedance spectroscopy has been performed on P2-Na2/3[Fe1/2Mn1/2]O2 half-cells operating in two different working voltage windows, one allowing and one preventing the high voltage phase transition occurring in P2-Na2/3[Fe1/2Mn1/2]O2 above 4.0 V vs Na+/Na; so as to unveil the transport properties at different states of charge and correlate them with the existing phases in P2-Na2/3[Fe1/2Mn1/2]O2. Supporting X-ray photoelectron spectroscopy experiments to elucidate the surface properties along with theoretical calculations have concluded that the formed electrode-electrolyte interphase is very thin and stable, mainly composed by inorganic species, and reveal that the structural phase transition at high voltage from P2- to “Z”/OP4-oxygen stacking is associated with a drastic increased in the bulk electronic resistance of P2-Na2/3[Fe1/2Mn1/2]O2 electrodes which is one of the causes of the observed capacity fading.

Coexistence of carbonyl and ether groups on oxygen-terminated (110)-oriented diamond surfaces

Diamond-based materials have unique properties that are exploited in many electrochemical, optical, thermal, and quantum applications. When grown via chemical vapor deposition (CVD), the growth rate of the (110) face is typically much faster than the other two dominant crystallographic orientations, (111) and (100). As such, achieving sufficiently large-area and high-quality (110)-oriented crystals is challenging and typically requires post-growth processing of the surface. Whilst CVD growth confers hydrogen terminations on the diamond surface, the majority of post-growth processing procedures render the surface oxygen-terminated, which in turn impacts the surface properties of the material. Here, we determine the oxygenation state of the (110) surface using a combination of density functional theory calculations and X-ray photoelectron spectroscopy experiments. We show that in the 0–1000 K temperature range, the phase diagram of the (110) surface is dominated by a highly stable phase of coexisting and adjacent carbonyl and ether groups, while the stability of peroxide groups increases at low temperatures and high pressures. We propose a mechanism for the formation of the hybrid carbonyl-ether phase and rationalize its high stability. We further corroborate our findings by comparing simulated core-level binding energies with experimental X-ray photoelectron spectroscopy data on the highest-quality (110)-oriented diamond crystal surface reported to date.