X-ray Photoelectron Spectroscopy In Order Research Articles

Sustainable Synthesis of N/S-Doped Porous Carbon from Waste-Biomass as Electroactive Material for Energy Harvesting

It is absolutely essential to convert biomass waste into usable energy in a rational manner. This investigation proposes the economical synthesis of heteroatom (N and S)-doped carbon (ATC) from Aesculus turbinata seed as a natural precursor by carbonization at 800 °C. The final product obtained was characterized using field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, high-resolution transmittance electron microscopy, X-ray diffraction, Raman spectroscopy, nitrogen adsorption-desorption isotherms, attenuated total reflectance Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy in order to investigate its structural property and chemical composition. The porous carbon achieved by this method contained oxygen, nitrogen, and sulfur from Aesculus turbinata seed and had pores rich in micropores and mesopores. Crystalline ATC obtained with a high surface area (560 m2 g−1) and pore size (3.8 nm) were exploited as electrode material for the supercapacitor. The electrochemical studies revealed a specific capacitance of 142 F g−1 at a current density of 0.5 A g−1 using 1 M H2SO4 as an electrolyte. ATC had exceptional cycling stability, and the capacitance retention was 95% even after 10,000 charge-discharge cycles. The findings show that ATC derived from biomass proved to be a potential energy storage material by converting waste biomass into a high-value-added item, a supercapacitor.

Improved Water-Gas Shift Performance of Au/NiAl LDHs Nanostructured Catalysts via CeO2 Addition.

Supported gold on co-precipitated nanosized NiAl layered double hydroxides (LDHs) was studied as an effective catalyst for medium-temperature water–gas shift (WGS) reaction, an industrial catalytic process traditionally applied for the reduction in the amount of CO in the synthesis gas and production of pure hydrogen. The motivation of the present study was to improve the performance of the Au/NiAl catalyst via modification by CeO2. An innovative approach for the direct deposition of ceria (1, 3 or 5 wt.%) on NiAl-LDH, based on the precipitation of Ce3+ ions with 1M NaOH, was developed. The proposed method allows us to obtain the CeO2 phase and to preserve the NiAl layered structure by avoiding the calcination treatment. The synthesis of Au-containing samples was performed through the deposition–precipitation method. The as-prepared and WGS-tested samples were characterized by X-ray powder diffraction, N2-physisorption and X-ray photoelectron spectroscopy in order to clarify the effects of Au and CeO2 loading on the structure, phase composition, textural and electronic properties and activity of the catalysts. The reduction behavior of the studied samples was evaluated by temperature-programmed reduction. The WGS performance of Au/NiAl catalysts was significantly affected by the addition of CeO2. A favorable role of ceria was revealed by comparison of CO conversion degree at 220 °C reached by 3 wt.% CeO2-modified and ceria-free Au/NiAl samples (98.8 and 83.4%, respectively). It can be stated that tuning the properties of Au/NiAl LDH via CeO2 addition offers catalysts with possibilities for practical application owing to innovative synthesis and improved WGS performance.

Correlating hydrophobicity to surface chemistry of microstructured aluminium surfaces

Highly hydrophobic aluminium surfaces fabricated by chemical etching are investigated by Contact Angle Goniometry, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy in order to correlate the wettability of our samples with their morphology at the sub-micrometer scale and with the chemical composition of the very first surface layers. We find that the etched aluminium surfaces have binary structures with nanoscale block-like convexities and hollows, which provide more space for air trapping. We also demonstrate that both hierarchical micro/nanostructures and surface composition endow these surfaces with excellent hydrophobic properties. XPS analysis shows indeed that the contact angle anti-correlates with the amount of metallic aluminium present at the surface, but also confirms the essential role of the adsorption of airborne carbon compounds. The hydrophobic behaviour depends therefore on the combined effects of surface morphology and surface chemistry.

Straightforward Solution Polymerization Synthesis of Porous Carbon@Gold Nanoparticles Electrode for High-Performance Supercapacitor

Porous carbon materials have proven to be an excellent candidate electrode material for supercapacitor applications; however, the energy density is relatively in a low level. In this work, we introduce gold nanoparticles into the precursor of polyacrylonitrile to prepare composite materials of gold nanoparticles and porous carbon using a facile method to enhance the energy density of this carbon based supercapacitor device. The samples are quantitatively analyzed using transmission electron microscope, field emission scanning electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy in order to unveil the structure and morphological features. Accordingly, the results have confirmed the porous structure, including numerous micro/mesoporous, with relatively high specific surface area at 3, 305 m2/g. On the electrochemical analysis aspect, the composite materials demonstrated a high specific capacitance of 421.4 F/g at the current density of 0.5 A/g, which is much higher than that of the pristine carbon (without introducing gold nanoparticles), 190 F/g, indicating the optimized nature of the composite materials. Moreover, the symmetrical supercapacitor is assembled with composite electrode, and meshed with 6 M KOH aqueous solution as an electrolyte. Interestingly, a high specific energy of 10.4 Wh/kg is obtained at specific power of 124.9 W/kg. According to the findings, the obtained composite electrode material of gold nanoparticles and porous carbon is a highly promising electrode material for supercapacitors or other energy storage devices.

Preparation of uniformly dispersed N-isopropylacryl-amide/acrylic acid/nanosilver composite hydrogel and its anti-mold properties

To overcome the agglomeration tendency of nanosilver composite hydrogels and to improve their anti-mold properties, a method of preparing N-isopropylacrylamide/acrylic acid/nanosilver composite hydrogel was developed using the free radical polymerization method. The composite hydrogel was characterized via infrared spectroscopy, dynamic light scattering, transmission electron microscopy, and X-ray photoelectron spectroscopy in order to explore the effects of the acrylic acid content on particle size and dispersion properties of the composite hydrogels. The elemental composition, microstructure, and anti-mold properties of the bamboo strips treated with the composite hydrogel were also determined. The results showed that the composite hydrogel prepared using the novel method described in this study had good dispersity. Composite hydrogels with the smallest particle size and optimized dispersion were produced when AAc concentration was 0.64 µL/mL. The composite hydrogel effectively filled and covered the bamboo cells after treatment. Moreover, it displayed good anti-mold properties as well as retaining the color of the bamboo.

2-Mercaptobenzimidazole films formed at ultra-low pressure on copper: adsorption, thermal stability and corrosion inhibition performance

2-mercaptobenzimidazole (2-MBI) is considered as an effective corrosion inhibitor for copper. In this study, the adsorption of 2-MBI on pristine and pre-oxidized Cu(111) surfaces was investigated by sublimation at ultra low pressure, using Auger Electron Spectroscopy, Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy in order to understand its corrosion inhibition properties. 2-MBI adsorbs with S and N atoms bonded to Cu. On pristine Cu(111) surface, a self-assembled monolayer is formed at about 5 L, with the adsorption of atomic S resulting from molecule decomposition to form a (7×7)R19.1° structure, and that of the molecule forming a (8 × 8) structure. 2-MBI is lying flat in the adsorbed multilayer. Oxidation of copper prior to exposure results in compact and homogeneous molecular films, with dissociation and substitution of 2D oxide by 2-MBI, but much more slower than that for 2-mercaptobenzothiazole (2-MBT). A multilayer of 2-MBI can block the initial stages of oxidation of copper under low oxygen pressure at room temperature, and the molecular layer is stable until 500°C. The comparison with 2-MBT suggests that the latter is a better corrosion inhibitor for copper at room temperature.

2-Mercaptobenzothiazole corrosion inhibitor deposited at ultra-low pressure on model copper surfaces

Adsorption of 2-mercaptobenzothiazole (2-MBT) at ultra-low pressure and room temperature on metallic and pre-oxidized Cu(111) surfaces and its thermal stability were investigated using X-ray photoelectron spectroscopy in order to better understand the interfacial corrosion inhibiting properties. 2-MBT is lying flat in the monolayer with two sulphur atoms bonded to Cu and decomposes partially yielding atomic sulphur when interacting with metallic copper prior to forming molecular multilayers. Decomposition is prevented by surface pre-oxidation with 2D oxide dissociation accelerating the 2-MBT initial adsorption kinetics. 2-MBT further decomposes and partially desorbs above 100 °C. A pre-adsorbed 2-MBT monolayer on metallic copper inhibits surface corrosion.

Mass Transfer Thermodynamics through a Gas-Liquid Interface.

Molecular level information about thermodynamic variations (enthalpy, entropy, and free energy) of a gas molecule as it crosses a gas-liquid interface is strongly lacking from an experimental perspective under equilibrium conditions. Herein, we perform in situ measurements of water interacting with the ionic liquid (IL) 1-butyl-3-methylimidazolium acetate, [C4mim][Ace], using ambient pressure X-ray photoelectron spectroscopy in order to assess the interfacial uptake of water quantitatively as a function of temperature, pressure, and water mole fraction ( xw). The surface spectroscopy results are compared to existing bulk water absorption experiments, showing that the amount of water in the interfacial region is consistently greater than that in the bulk. The enthalpy and entropy of water sorption vary significantly between the gas-liquid interface and the bulk as a function of xw, with a crossover that occurs near xw = 0.6 where the water-IL mixture converts from being homogeneous ( xw < 0.6) to nanostructured ( xw > 0.6). Free energy results reveal that water at the gas-IL interface is thermodynamically more favorable than that in the bulk, consistent with the enhanced water concentration in the interfacial region. The results herein show that the efficacy for an ionic liquid to absorb a gas phase molecule is not merely a function of bulk solvation parameters but also is significantly influenced by the thermodynamics occurring across the gas-IL interface during the mass transfer process.

Study of the oxidation at the Al2O3/GaSb interface after NH4OH and HCl/(NH4)2S passivations and O2 plasma post atomic layer deposition process

In this work, the Al2O3/GaSb interface has been studied by x-ray photoelectron spectroscopy in order to improve interfacial and electrical properties of metal–oxide–semiconductor structures based on GaSb. First, different passivations using NH4OH or (NH4)2S were studied with a dilution of 4% and 5%, respectively, in order to reduce native oxides on the GaSb surface. Then, we considered the oxidation of the Al2O3 and GaSb surface after treatments with an oxygen (O2) plasma post atomic layer deposition (ALD) process and with post deposition annealing at different temperatures. We found that (NH4)2S passivation leads to a lower quantity of native oxides on the GaSb surface and that the O2 plasma post ALD process enables the formation of an oxygen-rich layer within the Al2O3 at the interface reducing the GaSb surface oxidation after post deposition annealing of the oxide.

X-ray photoelectron spectroscopy investigation of nanoporous NiO electrodes sensitized with Erythrosine B

Nanoporous NiO thin films were prepared onto FTO glass substrates by means of screen-printing and were sensitized with Erythrosine B (EryB) dye. The obtained material was electrochemically treated and characterized with ex-situ X-ray photoelectron spectroscopy in order to gain information beneficial to the application of sensitized NiO as photocathodes of p-type dye-sensitized solar cells (p-DSCs). In particular, EryB-sensitized NiO films underwent a series of electrochemical treatments in LiClO4/Acetonitrile (ACN) electrolyte devised so as to simulate possible conditions the electrode might encounter during operation in the photoelectrochemical cell. Upon potential-cycling in a range where the two NiO faradic events Ni(II)→Ni(III) and Ni(III)→Ni(IV) occur, X-ray photoelectron spectroscopy revealed that Erythrosine B dye experiences a partial detachment from the NiO surface. This detachment seems to be paralleled by the formation of stable (Ni)+(ClO4)− couples. Overall, the EryB dye displayed an acceptable electrochemical stability onto the surface of NiO electrode up to 50 cyclic voltammetries in the range −0.27÷+1.13V vs. Ag/AgCl. These results are useful for the evaluation of electrochemical stability of the dye when this is immobilized onto an electrode surface and are beneficial for a better comprehension of the degradation phenomena operating in real photoconversion device.

N and Al co-doping as a way to p-type ZnO without post-growth annealing

We demonstrate experimental results on p-type ZnO films grown by atomic layer deposition (ALD) and co-doped with aluminum and nitrogen (ANZO). The films were obtained at low temperature (100 °C) with different N to Al ratio and show conductivity type, which depends on the N and Al content. We applied the x-ray photoelectron spectroscopy in order to get insight into a chemical nature of dopants and we found three pronounced contributions of the N1s core level which appear at binding energies of 396.1, 397.4 and around 399 eV. Based on ANZO and undoped ZnO films, both grown by the ALD technique, the ZnO homojunction was obtained in one technological process without any post-growth high temperature processing. The rectification ratio as high as 4 × 104 at ± 2 V was achieved when an ultrathin Al2O3 layer was inserted between p- and n-type ZnO and a n-type ZnO buffer layer deposited on an insulating Si substrate was applied.

Hybrid co-deposition of molybdenum doped niobium pentoxide (NbxMoyOz) thin films

Mixed valent thin films, consisting of optically absorbing metallic cations within a dielectric matrix, possess a variety of optical and electronic properties that can be tailored through variation of dopant concentration and chemistry. This work details the reactive magnetron co-deposition of mixed valent NbxMoyOz thin films, systematically doped with optically absorbing Mo5+ cations, through adjustment of the molybdenum source power. Control over the concentration the Mo5+ valence state was achieved through decreases in the oxygen partial pressure facilitated via oxygen chemisorption by the molybdenum sputter flux at power levels of 0, 20, 40, 60, 80, and 100 W, while the Nb source was operated concurrently at a constant sputter power of 200 W. The resulting films, roughly 100 nm in thickness, were characterized using variable angle spectroscopic ellipsometry as well as x-ray photoelectron spectroscopy in order to derive a process-property relationship among molybdenum source power and its effects on the refractive index, extinction coefficient, optical band gap, as influenced by the relative concentrations of Mo5+, Mo6+, and Nb5+ cations. Increases in the molybdenum source power from 0 to 100 W allow for tailorability of the refractive index, 2.29 ≤ n550 ≤ 2.34, extinction coefficient, 0.00 ≤ k550 ≤ 0.02, and optical band gap, 3.05≤Eg ≤ 3.48 eV. The co-deposition procedure used within this work affords the ability to systematically adjust the content of the absorbing Mo5+ cations, from 0 to 3 at. %, within a dielectric matrix comprised of MoO3 and Nb2O5, presenting several opportunities in increasing the design-space for both optical coatings and electrochromic devices.

Au-loaded TiO2 and Ag-loaded TiO2 synthesized by modified sol–gel/impregnation method as photocatalysts

In this work, Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles were synthesized by modified sol–gel method together with impregnation method. The samples were characterized by their physicochemical properties using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy in order to obtain the correlation between structure and photocatalytic properties. XRD results indicated unloaded TiO2, Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles were all in the anatase phase with average crystallite size in the range of 10–13 nm. In addition, XPS analysis confirmed the presence of Au and Ag elements in Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles, respectively. The photocatalytic activities of TiO2, Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles were evaluated through the mineralization of formic acid under UV-light illumination. The results showed that Au-loading and Ag-loading could effectively improve the photocatalytic activities of TiO2. Furthermore, Au-loaded TiO2 exhibited a higher photocatalytic activity than Ag-loaded TiO2.

Enhancement of electrochemical and catalytic properties of MoS2 through ball-milling

MoS2 nanosheets of one to few layer thickness present novel electronic and enhanced catalytic properties with respect to the bulk material. Here we show that a simple and highly scalable ball-milling procedure can lead to significant improvements of the electrochemical and catalytic properties of the bulk natural MoS2. We characterized the material before and after the milling process by means of scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy in order to evaluate morphological and chemical features. We investigated the electrochemical properties by means of voltammetry techniques to monitor the electron transfer with [Fe(CN)6]4 −/3 − redox probe and the catalytic properties by monitoring the electrochemical hydrogen evolution reaction (HER). A significant overpotential lowering of about 210 mV is obtained for the HER by the ball-milled material when compared to bulk materials. This has a huge potential for the lowering of the energy consumption during hydrogen evolution. Ball-milling offers highly scalable dry method for large scale production of electrocatalyst with enhanced properties.

Heat treatment influence on the structural properties of supported Ni nanoclusters

Ni nanoclusters supported on Al2O3 were prepared using a coprecipitation method. A heat treatment at different temperatures was applied. The obtained samples were analyzed by X-ray diffraction (XRD), X-ray absorption spectroscopy and X-ray photoelectron spectroscopy in order to determine their global, local and electronic structures. The average particle size, the mean squares of the microstrain, the particle size and microstrain distribution functions of the supported Ni nanoclusters were determined by the XRD method using a generalized Fermi function for the approximation of the X-ray line. The recrystallization induced during the heat treatment process was analyzed. The present study indicated strong deformation of the local structure of the active metal in all of the samples investigated due to the metal-support interaction and the effects of the small particle size. Electronic structural investigations showed the presence of Ni in a metallic state as well as Ni2+ on the cluster surfaces.

Portable total reflection x-ray fluorescence analysis in the identification of unknown laboratory hazards

In this study, a portable total reflection x-ray fluorescence (TXRF) spectrometer was used to analyze unknown laboratory hazards that precipitated on exterior surfaces of cooling pipes and fume hood pipes in chemical laboratories. With the aim to examine the accuracy of TXRF analysis for the determination of elemental composition, analytical results were compared with those of wavelength-dispersive x-ray fluorescence spectrometry, scanning electron microscope and energy-dispersive x-ray spectrometry, energy-dispersive x-ray fluorescence spectrometry, inductively coupled plasma atomic emission spectrometry, x-ray diffraction spectrometry (XRD), and x-ray photoelectron spectroscopy (XPS). Detailed comparison of data confirmed that the TXRF method itself was not sufficient to determine all the elements (Z > 11) contained in the samples. In addition, results suggest that XRD should be combined with XPS in order to accurately determine compound composition. This study demonstrates that at least two analytical methods should be used in order to analyze the composition of unknown real samples.

Stability of reference masses: VI. Mercury and carbonaceous contamination on platinum weights manufactured at a similar time as the international and national prototype kilograms

The stability of prototype kilogram reference masses has been a long-standing question within the SI, with mass loss or gain at the surface being the principal concern. In papers I, III and IV of this series we showed mercury and organic carbonaceous contamination to be significant in sample surfaces exposed to typical prototype kilogram storage environments. In this work, we have examined the surfaces of six platinum mass standards manufactured in the mid-19th century. We used x-ray photoelectron spectroscopy in order to identify mercury and carbonaceous contamination, and assess the validity of our previous models for the rate of increase. We use white-light interferometry to study surface roughness and polishing damage. We see mercury on all six of the 19th century polished prototypes we analysed. For one weight, manufactured around 1830, we see a quantity of mercury roughly equivalent to 250 µg if present on the surface of a prototype kilogram at the same mass per unit area. The quantities of these contaminations calculated from our XPS spectra are in good agreement with the theoretical models developed in papers III and IV for the growth of mercury and carbonaceous contamination, respectively, and increase our confidence that these processes are indeed happening at the surface of polished kilogram prototypes in most (if not all) cases. We discuss some potential sources of mercury contamination, though the most likely source remains the accidental breakage of thermometers and barometers containing mercury in the past. Mercury in laboratory air can adsorb and diffuse into defects and grain boundaries, especially at polished surfaces. We consider some possible ways to improve the situation, for example by placing a gold foil in the proximity of a prototype to act as a ‘getter’ that will preferentially adsorb mercury.

Fabrication phosphomolybdic acid–reduced graphene oxide nanocomposite by UV photo-reduction and its electrochemical properties

Phosphomolybdic acid-reduced graphene oxide (PMoA-rGO) nanocomposites are fabricated by a photochemical reduction method. They are characterized by ultraviolet-visible spectra, scanning electron microscope images, Fourier transform infrared spectroscopy, Raman spectra and X-ray photoelectron spectroscopy in order to confirm that oxygen-containing functional groups on GO are replaced by PMoA and that GO is reduced to rGO in the photo-reduction process. The electrochemical properties of PMoA-rGO are investigated by cyclic voltammetry, which shows that the PMoA-rGO modified glassy carbon electrode has high electrocatalytic activity in acid solution via a fast, surface-controlled electron transfer process. The results indicate that the use of rGO not only increases the electroactive surface area, but also facilitates electron transfer due to its high electric conductivity.

Chemical and structural investigations of the interactions of Cu with MnSiO3 diffusion barrier layers

X-ray photoelectron spectroscopy (XPS) has been used to investigate the thermodynamic stability of Cu layers deposited onto Mn silicate (MnSiO3) barrier layers formed on SiO2 surfaces. Using a fully in situ growth and analysis experimental procedure, it has been shown that ∼1 nm Cu layers do not chemically react with ultra thin (∼2.6 nm) MnSiO3 surfaces following 400 °C annealing, with no evidence for the growth of Cu oxide species, which are known to act as an intermediate step in the Cu diffusion process into silica based dielectrics. The effectiveness of MnSiO3 as a barrier to Cu diffusion following high temperature annealing was also investigated, with electron energy loss spectroscopy suggesting that a ∼2.6 nm MnSiO3 layer prevents Cu diffusion at 400 °C. The chemical composition of a barrier layer formed following the deposition of a partially oxidised Mn (MnOx)/Cu alloy was also investigated using XPS in order to determine if the presence of Cu at the Mn/SiO2 interface during MnSiO3 growth inherently changes the chemical composition of the barrier layer. In contrast to previous publications, it has been shown that Mn oxide species do not form in the barrier region during thermal annealing, with Cu appearing to be chemically inert in the presence of Mn and SiO2.

Preparation, surface characteristics, and electrochemical double-layer capacitance of KOH-activated carbon aerogels and their O- and N-doped derivatives

Carbon aerogels are obtained by carbonizing organic aerogels prepared by polycondensation reaction of resorcinol or pyrocatechol with formaldehyde. They are KOH-activated at two KOH/carbon ratios to increase pore volume and surface area. Selected samples are also surface-treated to introduce oxygen and nitrogen functionalities. The objectives are to investigate the effect of porosity and surface functionalities on the electrochemical capacitance of the carbon and activated carbon aerogels. Samples are characterized by N2 and CO2 adsorption at −196 and 0 °C, respectively, immersion calorimetry, temperature-programmed desorption, and X-ray photoelectron spectroscopy in order to determine their surface area, porosity, and surface chemistry. Two series of samples are obtained: one micro-mesoporous and the other basically microporous. A surface area up to 1935 m2 g−1 was obtained after KOH activation. Electrochemical double-layer capacitance was studied by cyclovoltammetry and chronopotentiometry with a three-electrode cell, using Ag/AgCl as reference electrode. Gravimetric capacitance at 0.125 A g−1 is related to N2 adsorption-measured micropore volume and mean size and to particle density. The highest gravimetric capacitance, 220 F g−1, is obtained with two O- and N-doped samples. Volumetric capacitance of 123 F cm−3, double the value generally needed for applications in small-volume systems, is obtained with a largely microporous oxygen-doped activated carbon aerogel.