X-ray Photoelectron Spectroscopy Investigation Research Articles

Modeling and EXAFS investigation of U(VI) sequestration on Fe3O4/PCMs composites

Magnetite/porous carbonaceous materials (Fe3O4/PCMs) were synthesized simply by the hydrothermal method under nitrogen conditions. Various characterization, including scanning electron microscopy (SEM), X-ray diffraction spectra (XRD), Fourier transformed infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS), revealed that Fe3O4/PCMs composites contained plentiful oxygen-containing groups. The results of batch adsorption experiments displayed that U(VI) removal towards Fe3O4/PCMs composites was little influenced by ionic strength, revealing the inner-sphere complexation of U(VI) by Fe3O4/PCMs composites. The removal kinetics of U(VI) can be well fitted by the pseudo-second-order model. The maximum capture capacities of U(VI) on Fe3O4/PCMs reached 123.41 mg/g at 328 K. Moreover, the regeneration experiment showed that Fe3O4/PCMs composites exhibited good stability and recoverability for U(VI) capture. The capture mechanism of U(VI) on Fe3O4/PCMs involved adsorption and reduction by XPS and XANES investigation. In line with the EXAFS analysis, the U(VI) was partly reduced to U(IV) gradually with the increasing reaction time. The removal process of U(VI) on Fe3O4/PCMs composites was satisfactorily fitted by surface complexation modeling with an inner-sphere surface complexes. These results designated that Fe3O4/PCMs can be used as suitable adsorbents to eliminate uranium for environmental cleanup.

Effect of fluoride-mediated transformations on electrocatalytic performance of thermally treated TiO2 nanotubular layers

Abstract The peculiarities of morphology, crystalline structure and chemical composition of TiO 2 nanotubular layers (TNT) and TiO 2 nanoparticulate (NP) layers obtained by fluoride-mediated transformation of TNT have been described in the present paper. The annealing of amorphous TNT in a confined space under limited air access conditions leads to TNT-to-NP transformation accompanied by fluorine doping of the titania matrix as supported by X-ray photoelectron spectroscopy investigations. The collapse of tubular structure as well as the formation of nanoparticles was confirmed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Electrocatalytic activity of both TNT and NP electrodes toward oxygen reduction reaction (ORR) has been examined by cyclic voltammetry (CV). The positive shift of ORR wave of the NP layers in comparison with TNT makes the NP-based electrodes more suitable for oxygen reduction. The improved activity of the NP electrodes is attributed to the increased concentration of redox active Ti 3+ species owing to fluorine doping of TiO 2 which plays a crucial role in electroreduction of oxygen molecules.

Carbon Dioxide As Electrolyte Additive for Silicon-Based Lithium Ion Full Cells

Following up the great success of lithium ion batteries (LIBs) in the field of consumer electronics in the recent decades, LIBs are today also widely used as energy storage devices for various types of electric vehicles (EVs). However, it is believed that a substantial breakthrough of the electromobility can only take place, if EVs are able to achieve driving ranges of more than 500 km and, therefore, gaining greater consumer acceptance. To achieve these driving ranges, the energy content of the used LIBs needs to be increased to values of 350 Wh/kg and 750 Wh/L at the cell level. These improvements can be achieved by replacing the state-of-the-art graphite anode by high-capacity anode materials like silicon (Si), which is able to provide a nearly 10 times higher specific capacity compared to graphite.[1] However, due to huge volume changes of up to 300% upon lithiation/de-lithiation, Si-based anodes often suffer from poor cycling performance related to cracking and pulverization of the Si particles and continuous solid electrolyte interphase (SEI) re-formation. Typically, these issues are addressed by decreasing the size of the active material particles to the nanoscale (i.e. nanoparticles, nanowires or thin films) or the fabrication of composites like intermetallic Si phases or Si/carbon composite materials to decrease the overall volume changes.[2] Although these strategies are reported to be effective to improve the performance of Si electrodes, it was revealed that the dominating failure mechanism of full cells containing Si-based negative electrodes lies in the consumption active lithium from the cathode related to continuous electrolyte reduction at the Si negative electrode. The addition of appropriate electrolyte additives such as fluoroethylene carbonate (FEC) or vinylene carbonate (VC) can significantly improve the capacity retention and Coulombic efficiency of Si-based full cells by forming a more stable SEI on the Si negative electrode.[3, 4] Recently, Krause et al. demonstrated that the addition of carbon dioxide in the form of dry ice significantly improved the performance of Si-based full cells and even outperformed the most commonly used additive FEC.[5] However, the exact working mechanism of the carbon dioxide additive and especially the reductive decomposition reactions including the resulting morphology and/or chemical composition of the formed SEI layer are still uncertain. Within this study, thin film Si electrodes prepared via magnetron sputtering are employed as model electrodes (i.e. no binder or conductive additive) therefore, possible effects of the carbon dioxide can be correlated to the Si active material. These Si thin film electrodes are coupled with NMC-111 positive electrodes to Si/NMC-111 full cells, which are used for the electrochemical investigations. As the solubility of carbon dioxide in the organic carbonate based electrolytes is rather low, diethylpyrocarbonate is added to the baseline electrolyte, as pyrocarbonates are known as carbon dioxide generators and, therefore, the carbon dioxide is released in-situ within the assembled full cell. The addition of the diethylpyrocarbonate electrolyte additive leads to significantly improved performance of the Si/NMC-111 full cells in terms of Coulombic efficiency and capacity retention full cells during prolonged cycling compared to the baseline electrolyte. The chemical composition of the SEI layer formed on the Si negative electrodes is investigated by means of X-ray photoelectron spectroscopy (XPS). The XPS investigations reveal that the improved performance of the carbon dioxide containing cells is related the improved passivation of the negative electrode by the formation of mainly lithium carbonate at the Si surface. Reference s : [1] D. Andre, H. Hain, P. Lamp, F. Maglia, B. Stiaszny, Future high-energy density anode materials from an automotive application perspective, Journal of Materials Chemistry A, 5 (2017) 17174-17198. [2] M.N. Obrovac, V.L. Chevrier, Alloy Negative Electrodes for Li-Ion Batteries, Chemical Reviews, 114 (2014) 11444-11502. [3] R. Nölle, A.J. Achazi, P. Kaghazchi, M. Winter, T. Placke, Pentafluorophenyl Isocyanate as an Effective Electrolyte Additive for Improved Performance of Silicon-Based Lithium-Ion Full Cells, ACS Applied Materials & Interfaces, 10 (2018) 28187-28198. [4] M. Klett, J.A. Gilbert, S.E. Trask, B.J. Polzin, A.N. Jansen, D.W. Dees, D.P. Abraham, Electrode Behavior RE-Visited: Monitoring Potential Windows, Capacity Loss, and Impedance Changes in Li1.03(Ni0.5Co0.2Mn0.3)0.97O2/Silicon-Graphite Full Cells, Journal of The Electrochemical Society, 163 (2016) A875-A887. [5] L.J. Krause, V.L. Chevrier, L.D. Jensen, T. Brandt, The Effect of Carbon Dioxide on the Cycle Life and Electrolyte Stability of Li-Ion Full Cells Containing Silicon Alloy, Journal of The Electrochemical Society, 164 (2017) A2527-A2533.

XPS investigation on the reactivity of surface imine groups with TFAA

The chemical reaction of imine groups with vapors of trifluoroacetic anhydride (TFAA) was investigated in detail with X‐ray photoelectron spectroscopy (XPS) for the potential application in chemical derivatization (CD) studies of plasma treated surfaces. Imine groups were at first prepared by converting surface amine groups of a polymer precursor using a common vapor phase derivatization reaction with fluorine tagged aldehydes and ketones. The originally low yield for the imine forming reaction of approx. 50%, performed under standard conditions was dramatically enhanced up to 100% by an own developed procedure using a catalyst. This step allowed to obtain a consistent quantification and interpretation of the complex surface reaction products from different types of imine groups derivatized by TFAA.

Chemical Analysis of the Interface between Hybrid Organic-Inorganic Perovskite and Atomic Layer Deposited Al2O3.

Ultrathin metal oxides prepared by atomic layer deposition (ALD) have gained utmost attention as moisture and thermal stress barrier layers in perovskite solar cells (PSCs). We have recently shown that 10 cycles of ALD Al2O3 deposited directly on top of the CH3NH3PbI3–xClx perovskite material, are effective in delivering a superior PSC performance with 18% efficiency (compared to 15% of the Al2O3-free cell) with a long-term humidity-stability of more than 60 days. Motivated by these results, the present contribution focuses on the chemical modification which the CH3NH3PbI3–xClx perovskite undergoes upon growth of ALD Al2O3. Specifically, we combine in situ Infrared (IR) spectroscopy studies during film growth, together with X-ray photoelectron spectroscopy (XPS) analysis of the ALD Al2O3/perovskite interface. The IR-active signature of the NH3+ stretching mode of the perovskite undergoes minimal changes upon exposure to ALD cycles, suggesting no diffusion of ALD precursor and co-reactant (Al(CH3)3 and H2O) into the bulk of the perovskite. However, by analyzing the difference between the IR spectra associated with the Al2O3 coated perovskite and the pristine perovskite, respectively, changes occurring at the surface of perovskite are monitored. The abstraction of either NH3 or CH3NH2 from the perovskite surface is observed as deduced by the development of negative N–H bands associated with its stretching and bending modes. The IR investigations are corroborated by XPS study, confirming the abstraction of CH3NH2 from the perovskite surface, whereas no oxidation of its inorganic framework is observed within the ALD window process investigated in this work. In parallel, the growth of ALD Al2O3 on perovskite is witnessed by the appearance of characteristic IR-active Al–O–Al phonon and (OH)–Al=O stretching modes. Based on the IR and XPS investigations, a plausible growth mechanism of ALD Al2O3 on top of perovskite is presented.

Spectroscopic Ellipsometry and Electrochemical and X-ray Photoelectron Spectroscopy Investigation of the Influence of the Crystalline Plane on the Adsorption of α,ω-Alkanedithiols: Mono Versus Bi-Coordinated Configurations

The effect of the Au surface crystalline plane on the configuration of self-assembled monolayers (SAMs) of α,ω-alkanedithiols (DTs) is studied via reductive desorption (RD), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE) experiments. A remarkable difference in the SAM configuration of short DTs, such as 1,4-butanedithiol (C4DT) on both Au(111) and Au(100) is observed; while standing up (SU)-configured SAMs are formed on the (111) plane, lying down molecules form the structure on (100). The higher stability of the bi-coordinated structure on Au(100) is interpreted, indirectly, as higher bonding energies for the RS–Au(100) bond, in agreement with the RD and XPS results. Because hardly no SU phases are detected when adsorbing C4DT on Au(100), a longer DT is needed in order to achieve this configuration, namely, 1,6-hexanedithiol (C6DT). In this case, although the RSC6DT–Au(100) bond is similar to RSC4DT–Au(100) in the bi-coordinated phase, the larger lateral interactions in the S...

Hydrogen Evolution Reaction in an Alkaline Solution via ε-Fe3N Phase Formation on AISI 316 Stainless Steel by Plasma Treatment

Surface modification techniques can be used to enhance the use of low-cost materials in water electrolysis applications, improving their hydrogen evolution efficiency and life. In this work, a well-known AISI 316 stainless steel was treated with nitrogen direct current glow discharge plasma for the periods of 2, 3, 4, and 5 hours. The e-Fe3N phase was created from the first plasma treatment period, as detected by the X-ray powder diffraction and X-ray photo-electron spectroscopy investigations. To understand the effect of the e-Fe3N phase formation and growth on the hydrogen evolution rate and mechanism both the electrochemical and electro-chemical impedance spectroscopy measurements were done. Advanced plasma treatment over time and enhanced e-Fe3N phase growth were found to decrease the Tafel slope, over-potential, and polarization resistance, which contributes to improving the hydrogen evolution reaction properties of AISI 316 stainless steel. A lab scale electrolyzer equipped with a distilled water displacement attachment was prepared to evaluate the HER practically. The contact angle was measured to find an evidence on the effect of the advanced plasma treatment on the surface hydrophilicity.

Identifying the location of Cu ions in nanostructured SAPO-5 molecular sieves and its impact on the redox properties.

Combining X-ray Absorption Fine Spectroscopy (XAFS) with Anomalous Small-Angle X-ray Scattering (ASAXS) determines the location of Cu2+ ions in silicoaluminophosphate (SAPO-5) frameworks prepared by hydrothermal crystallization or impregnation. As expected, for the hydrothermally prepared sample, incorporation in the SAPO-5 framework was observed. For the first time preferential location of Cu2+ ions at the inner and outer surfaces of the framework is determined. Temperature-Programmed Reduction (TPR) and X-ray Photoelectron Spectroscopy (XPS) investigations demonstrated that such Cu2+ is stable in an argon (Ar) atmosphere up to 550 °C and can only be reduced under a hydrogen atmosphere. In contrast, Cu2+ deposited by impregnation on the pure SAPO-5 framework can be easily reduced to Cu+ in an Ar atmosphere. At lower Cu amounts, mononuclear tetrahedrally coordinated Cu species were formed which are relatively stable in the monovalent form. In contrast, at higher Cu amounts, CuO particles were found which change easily between the mono- and bivalent species.

Interaction of arsenic(III) and arsenic(V) on manganese dioxide: XPS and electrochemical investigations

Manganese dioxide (MnO2) synthesized by solid-state reaction was characterized and sorption of As(III) and As(V) on it was studied in batch mode using 76As radiotracer. Arsenic removal efficiency was ∼98 % in the pH range of 3–9. Solvent extraction study indicated that >95% of arsenic is present as As(V) after sorption. A new electrochemical method was developed for explaining the arsenic–manganese interactions. Cyclic voltammetry and chronopotentiometry measurements were carried out which indicated the difference in the interaction of As(III) and As(V) with MnO2. X-ray Photoelectron Spectroscopy (XPS) was carried out in which the 3p3/2 binding energy peak of As(III) and As(V) standards was compared with the binding energy peaks observed for arsenic sorbed on manganese dioxide. The binding energy peaks of arsenic on MnO2 were matching with that of As(V), irrespective of the oxidation state of arsenic taken for sorption. The study confirmed that irrespective of the initial oxidation state, arsenic was sorbed on MnO2 as As(V); during the oxidation of As(III) by MnO2, manganese was reduced to Mn(II) and the Mn(II) formed during sorption was sorbed on the surface creating fresh surface promoting further sorption. Based on the observations, a mechanism of sorption has been proposed.

Hard X-ray photoelectron spectroscopy investigation of annealing effects on buried oxide in GaAs/Si junctions by surface-activated bonding

Hard X-ray photoelectron spectroscopy measurements are performed on ≈10-nm-thick GaAs film/Si substrate junctions fabricated by the surface activated bonding and selective wet etching. The chemical shifts of GaO and AsO signals in Ga 2p3/2 and As 2p3/2 core spectra indicate that oxides are formed in a part of GaAs films neighboring GaAs/Si interfaces due to the surface activation process. Analyses of GaO and AsO signals show that the thickness of such buried oxides is decreased due to a post-bonding annealing at temperatures up to 400 °C. This means that the electrical properties of bonding interfaces, which are in the meta-stable states, are improved by the annealing. The thickness of oxides is different from that of amorphous-like transition layers at the GaAs/Si interfaces observed by transmission electron microscopy.

Pretreatment with a β-Cyclodextrin-Corrosion Inhibitor Complex Stops an Initiated Corrosion Process on Zinc.

Metal pretreatment is typically the first step in a reliable corrosion protection system. This work explores the incorporation of complexes between the cyclic oligosaccharide β-cyclodextrin (β-CD) and the molecular organic corrosion inhibitor 2-mercaptobenzothiazole (MBT) into an oxide-based pretreatment layer on metallic zinc. The layers were produced by a precorrosion step in the presence of β-CD. The resulting films have a morphology dominated by spherical particles. X-ray photoelectron spectroscopy investigations of the surfaces show the sulfur atoms of MBT to be partially oxidized but mostly intact. Samples pretreated with such a layer were subsequently coated with a model polymer coating, and the delamination of this model coating from an artificial defect was monitored by a scanning Kelvin probe (SKP). The SKP results show a slow down of delamination after several hours of the ongoing corrosion process for surfaces pretreated with the complexes. Finally, an increase in the electrode potential in the defect was observed, with a subsequent complete stop in delamination and repassivation of the defect after ≈10 h. This repassivation is attributed to the release of MBT after the initiation of the corrosion process. Most likely, the increase of pH, combined with the availability of aqueous solution, facilitates the MBT release after the initiation of a corrosion process. Consequently, complexes formed from β-CD and corrosion inhibitors can be effectively incorporated into inorganic pretreatments, and the inhibitor component can be released upon start of the corrosion process.

Surface behavior of low-temperature molten salt mixtures during the transition from liquid to solid

We report on surface investigations of cesium and tetraphenylphosphonium bis(trifluoromethylsulfonyl)imide (Cs[Tf2N], [PPh4][Tf2N]) molten salts and their mixtures. Depending on composition, these ionic compounds combine low melting points with exceptionally high thermal stability, and thus, exhibit considerably enlarged thermal operation windows compared to conventional ionic liquids. To elucidate their liquid-solid transition behavior in the near-surface region, temperature-dependent angle-resolved X-ray photoelectron spectroscopy (ARXPS) investigations were performed using our unique laboratory electron spectrometer DASSA (“Dual Analyzer System for Surface Analysis”), dedicated for investigations of macroscopic liquid samples. We followed temperature-induced changes in bulk and surface composition within the first nanometers of the neat salt melts and of Cs[Tf2N] : [PPh4][Tf2N] = 3 : 1 and 1 : 3 mixtures. In the mixtures, pronounced surface enrichment of Cs+ on expense of the bulky [PPh4]+ ions was found in the liquid state at temperatures close to the liquid-solid transition. In the solid state of Cs[Tf2N]-rich mixtures, [PPh4]+ completely vanishes from the near-surface region probed by XPS.

Fluorocarbon-Free Dual-Action Textile Finishes Based on Covalently Attached Thermoresponsive Block Copolymer Brush Coatings.

We present fluorocarbon-free block copolymer brushes as potential systems for dual-action, i.e., soil-repellent and soil-releasing textile finishes. Polymer brushes were prepared by employing specifically engineered triblock copolymers consisting of a hydrophobic, a hydrophilic, and either a central or a terminal anchor block bearing several anchoring groups for sustainable immobilization using the "grafting to" approach on both flat Si wafers and rough cotton fabrics. The switching characteristics of both types of block copolymer brushes were investigated by exposing the brushes to conditions and stimuli that are similar to those applied during laundering in a washing machine and drying in a laundry dryer, respectively. Contact angle measurements were performed to evaluate the polarity and wettability of the block copolymer brushes after treatment in hot water and in air, or in a vacuum at elevated temperatures simulating the washing and the drying procedure of a textile fabric. While the block copolymer brush with the terminal anchor showed only minor changes in terms of the wetting characteristics and the brush morphology upon the applied stimuli, the block copolymer brush with the central anchoring block exhibited a significant change from a hydrophilic (soil-releasing) to a hydrophobic (stain-repellent) surface. This switching behavior was reversible and could be achieved on both, flat Si wafers, and much more pronounced on rough cotton fabrics. Atomic force microscopy and angle-resolved X-ray photoelectron spectroscopy investigations further indicated a complete rearrangement of the brush morphology. Accordingly, we regard this type of block copolymer brushes as a system that fully meets the basic requirements for an application as a dual-action textile finish, which can be reversibly switched with respect to water repulsion.

Impact of the electrolyte salt anion on the solid electrolyte interphase formation in sodium ion batteries

Aiming at a more comprehensive understanding of the solid electrolyte interphase (SEI) in sodium ion batteries (NIBs), a detailed X-ray photoelectron spectroscopy (XPS) investigation of the few-nanometer thick passivation film formed on hard carbon (HC) in contact with various Na+-ion conducting electrolytes is reported. The electrolytes investigated include 1 M solutions of NaPF6, NaClO4, NaTFSI, NaFSI, and NaFTFSI, all dissolved in a common mixture of ethylene carbonate (EC) and diethylene carbonate (DEC) (EC/DEC = 1/1 wt. ratio). For comparison, the study of analogous Li-based electrolytes containing LiPF6 and LiFSI as representative electrolyte salts is also reported. The anion and cation of the electrolyte salt appear to play a key role in determining the overall SEI layer composition, including its depth evolution and thickness. The SEI building species formed on hard carbon by solvent reduction upon sodiation are found to decrease with the various salts in the order: NaPF6 > NaClO4 ≈ NaTFSI > NaFTFSI > NaFSI. The comparison of lithiated and sodiated HC electrodes shows that the SEI layer is more homogeneous and richer in organic species upon the use of Na-based electrolytes. Surface and depth-profiling XPS analysis on HC electrodes charged in the various electrolyte formulations provides in-depth insights on the differences and similarities of the SEI (composition, thickness, depth evolution, etc.) evolving from the variation in the chemical structure of the cations and anions of the respective salts.

Facile synthesis of polypyrrole encapsulated V2O5 nanohybrids for visible light driven green sonophotocatalytic degradation of antibiotics

The present work reports for the first time ultrasound-assisted facile synthesis of stable polypyrrole/vanadium oxide (Ppy/V2O5) nanohybrids using various loadings of the conducting polymer. Infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) investigations confirmed the formation of the nanohybrids via synergistic interaction between C of Ppy with O of V2O5. The loading of Ppy in the nanohybrids was found to be 15%, 30% and 45% respectively which was confirmed by thermogravimetric analysis (TGA) and scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) analyses. High resolution transmission electron microscopy (HR-TEM) revealed the formation of nanorods of V2O5 and a mixed morphology of spheres and rods in case of Ppy/V2O5 nanohybrids. X-ray diffraction (XRD) showed crystalline morphology of the nanohybrids but upon increasing the loading of Ppy up to 45%, the layered morphology of V2O5 was partially distorted. The band gap of Ppy/V2O5 nanohybrids was calculated to be 2.17eV, 2.16eV, and 2.14eV for Ppy/V2O5-15/85, Ppy/V2O5-30/70, and Ppy/V2O5-45/55 respectively from diffuse reflectance spectroscopy (DRS) studies. The surface area was determined by BET analysis and was found to be 25.91m2/g, 43.67m2/g, 53.51m2/g for Ppy/V2O5-15/85, Ppy/V2O5-30/70 and Ppy/V2O5-45/55 respectively. Highly efficient visible-light driven photocatalysis of Ppy/V2O5 nanohybrids was demonstrated by achieving 72–76% degradation of the antibiotics - ciprofloxacin (CIP) and erythromycin (E-mycin) within 50min. Radical trapping experiments validated that the photogenerated OH and O2− radicals were the two main photoactive species responsible for photocatalytic degradation. A plausible mechanism of photocatalytic degradation using Ppy/V2O5 nanohybrids under visible light irradiation is also proposed. Ppy was found to act as visible-light photosensitizer which aided the transfer of electrons to the conduction band of V2O5. The degraded drug fragments were identified using liquid chromatography–mass spectrometry (LC-MS).

Thermal cycling durability improved by doping fluorine to PrBaCo2O5+δ as oxygen reduction reaction electrocatalyst in intermediate-temperature solid oxide fuel cells

Double perovskite PrBaCo2O5+δ (PBC) has received much attention as cathode material for solid oxide fuel cells (SOFCs) due to its excellent catalytic activity for oxygen reduction reaction (ORR), especially at intermediate temperature up to 800 °C. However, its high thermal expansion coefficient (CTE), about twice as the electrolytes, usually results in poor durability. This work presents the effect of CTE reduction by doping fluorine ion to the oxygen-site of PrBaCo2O5+δ. The fluorine doping, which is confirmed with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy investigations, can substantially reduce CTE, from 24.03 × 10−6 K−1 down to 16.78 × 10−6 K−1 as determined with dilatometry while from 26.52 × 10−6 K−1 to 17.46 × 10−6 K−1 with high-temperature XRD. Consequently, the durability is improved by a factor of ∼3.0 when the electrodes are subjected to 200–800 °C thermal cycles. In addition, the fluorine doping does not deteriorate but maintains or even improves the oxygen transport properties and electrochemical performance for ORR of PBC, demonstrating that fluorine doping is very attractive for the development of promising cathode materials for intermediate-temperature SOFCs.

Combined DFT and XPS Investigation of Cysteine Adsorption on the Pyrite (1 0 0) Surface

The adsorption of cysteine on the pyrite (1 0 0) surface was evaluated by using first-principles-based density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS) measurements. The frontier orbitals analyses indicate that the interaction of cysteine and pyrite mainly occurs between HOMO of cysteine and LUMO of pyrite. The adsorption energy calculation shows that the configuration of the -OH of -COOH adsorbed on the Fe site is the thermodynamically preferred adsorption configuration, and it is the strongest ionic bond according to the Mulliken bond populations. As for Fe site mode, the electrons are found transferred from cysteine to Fe of pyrite (1 0 0) surface, while there is little or no electron transfer for S site mode. Projected density of states (PDOS) is analyzed further in order to clarify the interaction mechanism between cysteine and the pyrite (1 0 0) surface. After that, the presence of cysteine adsorption on the pyrite (1 0 0) surface is indicated by the qualitative results of the XPS spectra. This study provides an alternative way to enhance the knowledge of microbe–mineral interactions and find a route to improve the rate of bioleaching.

Selective Electrochemical Reduction of CO2 to CO on Zn-Based Foams Produced by Cu2+ and Template-Assisted Electrodeposition.

In this work, we aim to develop a Zn-based metal foam catalyst with very large specific area suitable for efficient CO production. Its manufacture is based on the dynamic hydrogen bubble template method that consists of the superposition of metal deposition and hydrogen evolution at the solid-liquid interface. We employed Cu ions in the Zn2+-rich electroplating bath as foaming agent. The concentration of Cu as foaming agent was systematically studied and an optimized Zn94Cu6 foam alloy was developed, which, to the best of our knowledge, is the most selective Zn-based CO2 electrocatalyst toward CO in aqueous bicarbonate solution (FECO = 90% at -0.95 V vs reversible hydrogen electrode). This high efficiency is ascribed to the combination of high density of low-coordinated active sites and preferential Zn(101) over Zn(002) texturing. X-ray photoelectron spectroscopy investigations demonstrate that the actual catalyst material is shaped upon reduction of an oxide/hydroxide-terminating surface under CO2 electrolysis conditions. Moreover, intentional stressing by oxidation at room conditions proved to be beneficial for further activation of the catalyst. Identical location scanning electron microscopy imaging before and after CO2 electrolysis and long-term electrolysis experiments also showed that the developed Zn94Cu6 foam catalyst is both structurally and chemically stable at reductive conditions.

2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate as an effective electron injecting interlayer on indium-tin oxide cathode in inverted bottom-emission organic light-emitting diodes

2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate (MADN:Rb2CO3) is used as an effective electron injecting interlayer on an indium-tin oxide (ITO) cathode for inverted bottom-emission organic light-emitting diodes (IBOLEDs). At a Rb2CO3 doping concentration of 20% in MADN, the device exhibits enhanced characteristics, some of which are turn-on voltage, luminance at a given current density, and current efficiency. The attained performance is better than that of the device using lithium fluoride (LiF) as an n-type dopant. Space-charge-limited current acknowledges improved electrical properties of Rb2CO3 doped MADN. Ultraviolet and X-ray photoelectron spectroscopy investigation unveils an interfacial dipole layer induced by charge transfer between Rb2CO3 and ITO, leading to a lowered ITO work function and an electron injection barrier. The improved electron injection and transport capabilities contribute to better charge balance in IBOLED, thus resulting in advanced luminance efficiency. In addition, the morphology stability of organic films is also amended, which benefits long-term reliability under operationally induced thermal stress. Moreover, the effectiveness of using Rb2CO3:MADN as an electron injecting layer for IBOLEDs is superior to many of its alkali-based counterparts demonstrated in the literature, with high compatibility with different types of sophisticated ITO-based IBOLEDs.

Dye-Sensitized Solar Cells Based on an N-Doped TiO2 and TiO2-Graphene Composite Electrode

In this work, the effect of graphene and nitrogen doping on the performance of dye-sensitized solar cells of pure TiO2 was studied. Pure and N-doped TiO2 nanoparticles were synthesized using a hydrothermal method, while graphene was prepared through the reduction of graphene oxide. The materials were characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), Raman, Brunauer–Emmett–Teller surface area analysis (BET) and ultraviolet-visible (UV-Vis) diffusion reflectance spectroscopy. Nitrogen dopant concentration varied from 0 at.% to 1.57 at.%. The results confirmed that all N-doped samples exhibited pure anatase phase with an average diameter in the range of 7–12 nm. The pore volume and BET surface area increased with the amount of nitrogen in TiO2. XPS investigation displayed an N1s peak around 397 eV, which suggested N-Ti-O structure in the TiO2 matrix. Moreover, optical measurements showed that the optical absorption edge of N-doped TiO2 exhibited a significant shift from ultraviolet to visible light region in comparison with pure TiO2. Dye-sensitized solar cells (DSSCs) were fabricated using N719 dye and various TiO2 based photoanodes. The photoanode of N-doped TiO2 modified with graphene showed the highest energy-conversion efficiency of 6.3%, while the efficiencies of pure and N-doped TiO2 cells are 0.41% and 1.21%, respectively. The improvement in conversion efficiency of graphene-based DSSC was attributed to the formed electron bridges between TiO2 and fluorine-doped tin oxide (FTO), which led to a reduction in the recombination rate of electron-hole pairs and an increase in the rate of electron transport.