Surface Oxidation State Research Articles

Fabrication of Nanoporous IrO₂/Ir Films for Bioelectrode and Neural Prosthesis Applications.

IrO₂ and Ir are attractive materials for bio-interface applications due to their desirable stability, electrochemical performance, and biocompatibility. Nanostructured IrO₂/Ir possesses several advantageous properties including large surface-to-volume ratio, light weight, super hydrophilic surface, desirable electrochemical capability, and cell adhesion. Herein, we employ a cost-effective process to fabricate uniform nanoporous IrO₂/Ir film by chemical bath deposition, high-vacuum annealing, and electrochemical activation. High-vacuum annealing can remove oxygen from an IrO₂ film to create a nanoporous structure, and we determine the optimized electrochemical activation to transform Ir to IrO₂/Ir. The surface morphology, roughness, hydrophilicity, crystallinity, oxidation state, and charge storage capacity (CSC) of the films were analyzed. The nanoporous IrO₂/Ir film showed a 25% increase of CSC compared to the dense IrO₂ film, and this excellent performance makes it a promising candidate for bio-interface applications. In addition, this fabrication route can be cost-effective process without wasting the expensive noble metal Ir material.

Zinc and nitrogen ornamented bluish white luminescent carbon dots for engrossing bacteriostatic activity and Fenton based bio-sensor

Carbon dots with heteroatom co-doping associated with consummate luminescence features are of acute interest in diverse applications such as biomolecule markers, chemical sensing, photovoltaic, and trace element detection. Herein, we demonstrate a straightforward, highly efficient hydrothermal dehydration technique to synthesize zinc and nitrogen co-doped multifunctional carbon dots (N, Zn-CDs) with superior quantum yield (50.8%). The luminescence property of the carbon dots can be tuned by regulating precursor ratio and surface oxidation states in the carbon dots. A unique attribution of the as-prepared carbon dots is the high monodispersity and robust excitation-independent emission behavior that is stable in enormously reactive environment and over a wide range of pH. These N, Zn-CDs unveils captivating bacteriostatic activity against gram-negative bacteria Escherichia coli. Furthermore, the excellent luminescence properties of these carbon dots were applied as a platform of sensitive biosensor for the detection of hydrogen peroxide. Under optimized conditions, these N, Zn-CDs reveals high sensitivity over a broad range of concentrations with an ultra-low limit of detection (LOD) indicating their pronounced prospective as a fluorescent probe for chemical sensing. Overall, the experimental outcomes propose that these zero-dimensional nano-dots could be developed as bacteriostatic agents to control and prevent the persistence and spreading of bacterial infections and as a fluorescent probe for hydrogen peroxide detection.

In Situ UV-Visible Assessment of Iron-Based High-Temperature Water-Gas Shift Catalysts Promoted with Lanthana: An Extent of Reduction Study

The extent of reduction of unsupported iron-based high-temperature water-gas shift catalysts with small (<5 wt %) lanthana contents was studied using UV-visible spectroscopy. Temperature- programmed reduction measurements showed that lanthana content higher than 0.5 wt % increased the extent of reduction to metallic Fe, while 0.5 wt % of lanthana facilitated the reduction to Fe3O4. In situ measurements on the iron oxide catalysts using mass and UV-visible spectroscopies permitted the quantification of the extent of reduction under temperature-programmed reduction and high-temperature water-gas shift conditions. The oxidation states were successfully calibrated against normalized absorbance spectra of visible light using the Kubelka-Munk theory. The normalized absorbance relative to the fully oxidized Fe2O3 increased as the extent of reduction increased. XANES suggested that the average bulk iron oxidation state during the water-gas shift reaction was Fe+2.57 for the catalyst with no lanthana and Fe+2.54 for the catalysts with 1 wt % lanthana. However, the UV-vis spectra suggest that the surface oxidation state of iron would be Fe+2.31 for the catalyst with 1 wt % lanthana if the oxidation state of iron in the catalyst with 0 wt % lanthana were Fe+2.57. The findings of this paper emphasize the importance of surface sensitive UV-visible spectroscopy for determining the extent of catalyst reduction during operation. The paper highlights the potential to use bench-scale UV-visible spectroscopy to study the surface chemistry of catalysts instead of less-available synchrotron X-ray radiation facilities.

Elucidating Surface Restructuring-Induced Catalytic Reactivity of Cobalt Phosphide Nanoparticles under Electrochemical Conditions

Probing and understanding surface restructuring-induced electrocatalytic reactivity is an essential but challenging step toward rational prediction of electrocatalytic properties and design of high-performance catalysts. Cobalt phosphide (CoP) nanoparticles are state-of-the-art electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). However, the structure–reactivity correlations are not straightforward because the nanoparticles will restructure under working conditions. Employing a protective sample transfer procedure, we use simple lab XPS to unveil the changes in oxidation state and composition of the nanoparticle surface induced by electrochemical reaction conditions. CoP nanoparticles are naturally oxidized on their surface. In alkaline electrolyte under HER conditions, a Co-rich phosphide surface is generated as a result of polyphosphate dissolution and reduction of the oxidized P and Co species. In alkaline electrolyte under OER conditions, an oxidati...

Surface Oxidation of Graphene Oxide Determines Membrane Damage, Lipid Peroxidation, and Cytotoxicity in Macrophages in a Pulmonary Toxicity Model.

While two-dimensional graphene oxide (GO) is used increasingly in biomedical applications, there is uncertainty on how specific physicochemical properties relate to biocompatibility in mammalian systems. Although properties such as lateral size and the colloidal properties of the nanosheets are important, the specific material properties that we address here is the oxidation state and reactive surface groups on the planar surface. In this study, we used a GO library, comprising pristine, reduced (rGO), and hydrated GO (hGO), in which quantitative assessment of the hydroxyl, carboxyl, epoxy, and carbon radical contents was used to study the impact on epithelial cells and macrophages, as well as in the murine lung. Strikingly, we observed that hGO, which exhibits the highest carbon radical density, was responsible for the generation of cell death in THP-1 and BEAS-2B cells as a consequence of lipid peroxidation of the surface membrane, membrane lysis, and cell death. In contrast, pristine GO had lesser effects, while rGO showed extensive cellular uptake with minimal effects on viability. In order to see how these in vitro effects relate to adverse outcomes in the lung, mice were exposed to GOs by oropharyngeal aspiration. Animal sacrifice after 40 h demonstrated that hGO was more prone than other materials to generate acute lung inflammation, accompanied by the highest lipid peroxidation in alveolar macrophages, cytokine production (LIX, MCP-1), and LDH release in bronchoalveolar lavage fluid. Pristine GO showed less toxicity, whereas rGO had minimal effects. We demonstrate that the surface oxidation state and carbon radical content play major roles in the induction of toxicity by GO in mammalian cells and the lung.

Effect of Substrate Temperature on the Microstructural, Morphological, and Optical Properties of Electrosprayed ZnO Thin Films

Polycrystalline ZnO thin films were prepared on silicon substrates using electrospray method with vertical setup. Water and ethanol were used as solvents for zinc acetate dehydrate and no postdeposition annealing was required for formation of ZnO. The influence of substrate temperature in the range of 150–250°C on surface morphology and roughness was studied by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and optical profilometry. An improvement of surface quality and smoothing of the films with temperature were obtained. X-ray diffraction measurements revealed that, at all investigated substrate temperatures, the films were polycrystalline with crystallites’ sizes decreasing with temperature. Besides, the preferred crystal orientation varies with the substrate temperature. The analysis of surface chemical composition and oxidation state was performed with X-ray photoelectron spectroscopy (XPS). It was shown that, at substrate temperature of 200°C, the deposited ZnO films were closest to the stoichiometric ones. In general, the films at 150°C were oxygen-deficient, while at other studied temperatures, the films had excess of oxygen more pronouncedly at 200°C. Spectral ellipsometric measurements confirmed that the structural disorder is the highest at 150°C and improves with temperature. Refractive indexes for films at 200°C and 250°C are almost the same, 1.97 and 1.93, respectively, at wavelength of 600 nm, while for the sample deposited at 150°C, the refractive index is substantially lower, 1.67. The optical band gap is slightly influenced by the substrate temperature: 3.27 eV at 150°C and 3.32 eV at 200°C.

Cosputtered Calcium Manganese Oxide Electrodes for Water Oxidation.

Calcium manganese oxide films were prepared by cosputter deposition from Mn and CaMnO3 targets and evaluated for their suitability as catalysts for the oxygen evolution reaction (OER). Scanning electron microscopy (SEM) revealed a compact morphology for the as-deposited films and the formation of nanorodlike features on the surfaces after annealing at 600 °C. X-ray-photoelectron-spectroscopy analysis showed that the surface oxidation state is close to +III (as in Mn2O3) for the as-deposited films and increases slightly to a mixture of III and IV after annealing occurs in dry air at 400-600 °C. Glancing-incidence X-ray diffraction (GIXRD) suggested that the CaMnxOy films are amorphous even when heated to 600 °C. However, transmission electron microscopy (TEM) showed that there is actually a polycrystalline component of the film, which best matches Mn3O4 (hausmannite with the average Mn oxidation state of ∼+2.7) but may have a slightly expanded unit cell because of the incorporation of Ca. Electrochemical analyses revealed that the as-deposited CaMnxOy films were OER-inactive. In contrast, annealing at 400 or 600 °C resulted in an increase of ∼15-fold in the current densities, which reached j ≅ 1.5 mA·cm-2 at OER overpotentials of η ≈ 550 mV in cyclic voltammetry (CV) sweeps. For the same η, annealed CaMnxOy electrodes also showed good electrochemical stabilities during 2 h of electrolysis, as rather constant steady-state current densities of j ≅ 0.4-0.5 mA·cm-2 were observed. The thicknesses and surface morphologies of the CaMnxOy films did not change during the electrochemical measurements, indicating that corrosion was negligible. In comparison with a previous study in which Ca-free thin layers of MnOx were evaluated, the results demonstrate that Ca2+ incorporation can enhance the OER activity of MnOx electrocatalysts prepared by sputter deposition. This work provides guidance for designing new electrodes for water oxidation on the basis of the abundant and nontoxic elements manganese and calcium.

Synthesis and catalytic activity of Ag nanoparticles dispersed on nitrogen-doped GOPx toward direct electrooxidation of formaldehyde

Silver nanoparticles (Ag NPs) were synthesized and dispersed on the electronically conductive and electrochemically accessible surface of a GOPx composite, which was then employed as a probe for formaldehyde (HCHO) oxidation. The surface nanostructure, crystallographic properties, and oxidation state of the metal present in the GOPx-Ag nanocomposite were investigated using high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. HCHO electrooxidation was evidenced by the appearance of a very well defined anodic peak with an onset potential of −0.783V, which is unique in the literature. The effect of various electroanalytical parameters like concentration, scan rate, and upper potential limit was investigated toward HCHO electrooxidation on GOPx-Ag catalyst. Amperometric study showed remarkable HCHO electrooxidation response with a wide linear range of 1μM–70mM, limit of detection (LOD) 0.167μM, limit of quantification (LOQ) 0.556μM and sensitivity of 35.74μAmM−1cm−2. The experimental results further indicated the long-term stability and practical feasibility of the GOPx-Ag catalyst, with excellent recoveries for HCHO oxidation. The remarkable catalytic efficiency and anti-poisoning properties were far superior to those of many previously reported HCHO sensors. The astonishing analytical performance of GOPx-Ag opens up a new path for fabricating promising HCHO sensors.

Dynamic surface composition in a Mars-van Krevelen type reaction: CO oxidation on Au/TiO2

Aiming at a better mechanistic understanding of Mars-van Krevelen type catalytic reactions, we have systematically investigated possible correlations between the composition of the reaction gas atmosphere, the concentration of surface oxygen vacancies (surface oxidation state), and the catalytic activity of a Au/TiO2 catalyst in the CO oxidation reaction. In the meantime, there is considerable experimental and theoretical evidence that this reaction follows a Au-assisted Mars-van Krevelen mechanism at reaction temperatures ≥80 °C. Employing quantitative pulse experiments in a temporal analysis of products (TAP) reactor we found that both the surface oxidation state and the activity of the catalyst under steady-state conditions depend sensitively on the composition of the reaction gas atmosphere, specifically on the CO:O2 ratio, and that there is a strict correlation between these quantities. A simple kinetic model is introduced, which allows to quantitatively determine the ratio of the effective reaction rate constants for reduction and oxidation of the TiO2 support surface. These results and ideas are considered to be of general relevance for the understanding of Mars-van Krevelen type reactions and specifically of oxidation reactions on supported Au catalysts, and they lend further support to previous proposals of a Au-assisted Mars-van Krevelen mechanism for this reaction.

Multicolor Spectral-Specific Silicon Nanodetectors based on Molecularly Embedded Nanowires.

Silicon-based photodetectors cannot distinguish between different wavelengths. Therefore, these detectors relay on color-specific filters to achieve color separation. Color filters add complexity to color sensitive device fabrication, and hinder miniaturization of such devices. Here, we report an ultrasmall (as small as ∼20 nm by 300 nm), red-green-blue-violet (RGBV) filter-free spectrally gated field effect transistor (SGFET) detectors. These photodetectors are based on organic-silicon nanowire hybrid FET devices, capable of detecting specific visible wavelength spectrum with full width at half-maxima (fwhm) under 100 nm. Each SGFET is controlled by a distinctive RGBV spectral range, according to its specific organic fluorophore functionalization. The spectral-specific RGBV detection is accomplished via covalent attachment of different fluorophores. The fluorophore molecules inject electrons into the nanowire structure as a result of light absorption at the appropriate RGBV spectral range. These photoinduced electrons modify the occupancies of the oxide's surface states, shifting the device threshold voltage, thus changing its conductivity, and functioning as a negative stress bias in a p-type SiNW FETs. A positive biasing can be achieved via UV light-induced ionization, which leads to detrapping and translocation of electrons at the oxide layer. Furthermore, a novel theoretical model on the mechanism of action of these devices was developed. Also, we show that suspended SGFETs can function as nonvolatile memory elements, which unlike fast-relaxing on-surface SGFETs, can store discrete "on" (RGBV illumination) and "off" (UV illumination) states for several days at ambient conditions. We also demonstrate a unique single-nanowire multicolor photodetector, enabling in principle a broad spectral detection over a single silicon nanowire element. These highly compact, spectral-controlled nanodevices have the potential to serve in various future novel optoelectric applications.

Lanthanide-doped W18O49 nanowires: Synthesis, structure and optical properties

The effects of Ce- and La-doped WOx nanostructures on the morphology and crystal structures of WOx nanowires are investigated first, then the impact of these dopants on the cathodoluminescence (CL) properties of the WOx nanowires is studied. The dopants induced a morphological evolution and crystalline lattice expansion of the WOx nanostructures. By analyzing the surface composition and oxidation state ratios of W5+/W6+ in each sample using X-ray photoelectron spectroscopy, we attempt to interpret the observed CL spectra shift from ultraviolet to blue emission of the Ce- and La-doped nanowires.

The structure of reconstructed chalcopyrite surfaces

Chalcopyrite (CuFeS2) surfaces are of major interest for copper exploitation in aqueous solution, called leaching. Since leaching is a surface process knowledge of the surface structure, bonding pattern and oxidation states is important for improving the efficiency. At present such information is not available from experimental studies. Therefore a detailed computational study of chalcopyrite surfaces is performed. The structures of low-index stoichiometric chalcopyrite surfaces {hkl} h, k, l ∈ {0, 1, 2} have been studied with density functional theory (DFT) and global optimization strategies. We have applied ab initio molecular dynamics (MD) in combination with simulated annealing (SA) in order to explore possible reconstructions via a minima hopping (MH) algorithm. In almost all cases reconstruction involving substantial rearrangement has occurred accompanied by reduction of the surface energy. The analysis of the change in the coordination sphere and migration during reconstruction reveals that S-S dimers are formed on the surface. Further it was observed that metal atoms near the surface move toward the bulk forming metal alloys passivated by sulfur. The obtained surface energies of reconstructed surfaces are in the range of 0.53–0.95 J/m2.

Electrodeposited Cu-Sn Alloy for Electrochemical CO2 Reduction to CO/HCOO\u2212

Cu-Sn alloy electrodes were prepared by simple electrodeposition method for the electrochemical reduction of CO2 into CO and HCOO−. The alloy electrode surfaces provided good selectivity and efficiency in electrochemical CO2 conversion because they provided appropriate binding energies between the metal and the reactive species obtained through CO2 reduction. Therefore, product selectivity can be modulated by altering the Cu-Sn crystal structure of the electrode. Using the Cu-Sn alloy electrodes, electrochemical reduction was performed at applied potentials ranging from − 0.69 to − 1.09 V vs. reversible hydrogen electrode (RHE). During electrochemical CO2 reduction, all the prepared Cu-Sn alloy electrodes showed prominent suppression of hydrogen evolution. In contrast, Cu87Sn13 has high selectivity for CO formation at all the applied potentials, with maximum faradaic efficiency (FE) of 60% for CO at − 0.99 V vs. RHE. On the other hand, Cu55Sn45 obtained a similar selectivity for electrodeposition of Sn, with FE of 90% at − 1.09 V vs. RHE. Surface characterization results showed that the crystal structure of Cu87Sn13 comprised solid solutions that play an important role in increasing the selectivity for CO formation. Additionally, it suggests that the selectivity for HCOO− formation is affected by the surface oxidation state of Sn rather than by crystal structures like intermetallic compounds.Graphical The Cu-Sn alloy catalysts prepared by simple electrodeposition can control the selectivity for CO and HCOO− formation by tuning its crystal structure. Surface analyses revealed that solid solutions and the oxidation state of Sn play an important role in the formation of CO and HCOO− upon CO2 reduction, respectively.

Self-catalytic stabilized Ag-Cu nanoparticles with tailored SERS response for plasmonic photocatalysis

In-situ SERS monitoring of direct plasmon-driven photocatalysis was achieved using relatively earth-abundant Cu NPs following their decoration with tiny amounts of silver, which promoted excellent SERS and high catalytic activity. The SERS and catalytic performance of the Ag-Cu NPs can be tuned by changing their composition. In particular, it was found that the surface oxidation state of copper could be switched to its metallic state via self-plasmon catalysis under laser irradiation, highlighting the potential of air-unstable copper NPs as stable plasmonic catalysts. These dual functional Ag-Cu NPs were used for SERS real-time monitoring of plasmon-driven photocatalysis reactions involving the degradation of Rhodamine 6G and the dimerization of 4-nitrothiophenol. The corresponding catalytic reaction mechanisms were discussed.

Phosphate-dependent modulation of antibacterial strategy: a redox state-controlled toxicity of cerium oxide nanoparticles

Specific reactivity of cerium oxide nanoparticles with phosphate ions was used to design a novel antibacterial system. The redox sensitivity of cerium oxide nanoparticles (CeNPs) was used to irreversibly scavenge phosphate ions from the microbial growth media resulting in nutrient starvation in microbes. Cerium oxide nanoparticles surface was engineered with different ratios of ( $$\hbox {Ce}\,{(+3)}/\hbox {Ce}\,{(+4)})$$ cerium oxidation states and the effect of surface oxidation states was evaluated on the antibacterial activity. The nutrient depletion-based antibacterial activity is demonstrated selectively by CeNPs with higher $$\hbox {Ce}\,{(+3)}/\hbox {Ce}\,{(+4)}$$ ratio on the surface. The surface chemistry of $$\hbox {Ce}\,{(+3)}$$ is altered in the presence of phosphate, resulting in the irreversible formation of surface cerium phosphates leading to the loss of its intrinsic superoxide dismutase (SOD) activity. It is hypothesized that nutrient starvation by $$\hbox {Ce}\,{(+3)}$$ leads to oxidative stress in microbes which is not neutralized by the altered surface chemistry of CeNPs with high $$(\hbox {Ce}\,{(+3)}/\hbox {Ce}\,{(+4)})$$ ratio. On the contrary, CeNPs with higher $$(\hbox {Ce}\,{(+4)}/\hbox {Ce}\,{(+3)})$$ ratio did not show any reactivity towards phosphate, thus depicted no antibacterial activity, confirming the hypothesis that surface chemistry, rather than size or morphology-dependent toxicity is the main reason for the observed antibacterial activity of CeNPs.

Silver Nanoparticles with Surface-Bonded Oxygen for Highly Selective CO2 Reduction

The surface electronic structures of catalysts need to be carefully engineered in CO2 reduction reaction (CO2RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lowers the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO2RR reaction intermediates, which may significantly improve the catalytic activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO2RR performances. A comparative investigation on air-annealed Ag (Air-Ag) catalyst with or without the post-treatment of H2 thermal annealing (H2-Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O–Agδ+) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rat...

Anodic behavior of uranium in AlCl3-1-ethyl-3-methyl-imidazolium chloride ionic liquid

Abstract The oxidation state of metals unambiguously affects its anodic behavior in ionic liquid. We systematically investigated the anodic behavior of uranium with different surface oxidation states by electrochemical measurements, spectroscopic methods and surface analysis techniques. In the anodic process, metal uranium can be oxidized to U3+. The corresponding products accumulated on the metal/ILs interface will form a viscous layer. The anodic behavior of uranium is also strongly dependent upon the surface oxide states including thickness and homogeneity of the oxide film. With an increase in the thickness of oxide film, it will be breached at potentials in excess of a critical value. A uniform oxide on uranium surface can be breached evenly, and then the underlying metal starts to dissolve forming a viscous layer which can facilitate uniformly stripping of oxide, thus giving an oxide-free surface. Otherwise, a nonuniform oxide can result in a severe pitted surface with residue oxygen.

ORR Electrocatalysts with a Low Pt Loading Comprising Hierarchical Graphene-Based Supports

This report presents a new family of electrocatalysts (ECs) for the oxygen reduction reaction (ORR) that comprises hierarchical graphene-based supports (H-GRs). The ECs, which are intended for application at the cathode of proton-exchange membrane fuel cells (PEMFCs), exhibit a “core-shell” morphology. The “core” is the H-GR support, which is covered by a carbon nitride “shell”. The latter bears “coordination nests”, which stabilize the ORR active sites [1]. The H-GRs consist of two components, namely: (i) high defected graphene nanoplatelets, which are supported on ZnO nanoparticles (NPs) [2]; and (ii) carbon black, that acts as spacer and facilitates the charge and mass transport phenomena that take place during the operation of the ECs. Two groups of ECs are synthesized, I and II. I includes the pristine H-GR support; II comprises H-GR suitably treated to etch the ZnO NPs. Both I and II are characterized by a very low loading of platinum, on the order of ca. 3 wt%, that is the “active metal” in the ORR active sites [1]. Ni and Cu are introduced as “co-catalysts” to improve the ORR performance [1]. All the ECs undergo an extensive post-synthesis activation process (A), that significantly affects their chemical composition, structure and morphology. As a result, a remarkable ORR performance is achieved that is significantly improved in comparison with state-of-the-art Pt/C reference ECs. The proposed ECs are extensively characterized both before and after A to study the complex interplay between the synthetic parameters, the physicochemical properties, and the electrochemical ORR performance both “ex-situ” and in single PEMFC. In this regard, particular attention is dedicated to clarify the role played by the graphene nanoplatelets included in the H-GR support. Inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and CHNOS microanalyses are adopted to determine the bulk chemical composition of the ECs. The surface composition and oxidation states are probed with X-ray photoelectron spectroscopy (XPS), while the structure of the ECs is investigated through wide-angle X-ray diffraction (WAXD) and vibrational spectroscopies (e.g., confocal micro-Raman). High-resolution transmission electron microscopy (HR-TEM) is used to study the morphology. Cyclic voltammetry with the rotating ring-disk electrode (CV-TF-RRDE) allows the details of the ORR performance and mechanism to be elucidated. Finally, the ECs are used to fabricate membrane-electrode assemblies (MEAs) that are tested in single PEMFC in operating conditions. Acknowledgements This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 696656. The authors thank the Strategic Project “From materials for Membrane electrode Assemblies to electric Energy conversion and SToRAge devices” (MAESTRA) of the University of Padova for funding this research.

Orbital orientation mapping of V2O5 thin films

We report the effects of growth methods on the orbital orientation in vanadium pentoxide (V2O5) thin films, an important factor to consider when selecting growth techniques for highly selective catalysts and devices. Thermal evaporation and sol-gel methods were used to synthesize the V2O5 films. The surface morphology, roughness, and orientation of the films were characterized by atomic force microscopy and x-ray diffraction. Surface electronic properties and oxidation states were assessed by x-ray photoemission spectroscopy. Polarized x-ray absorption spectroscopy demonstrated that the thermally evaporated film [which was in the (001) orientation] exhibited greater anisotropy than the (100) oriented sol-gel film. The observed increase in anisotropy agrees well with computational findings which revealed that more vanadyl bonds are present at the surface of the thermally evaporated film than at the surface of the sol-gel film. The same computational study also found that the orientation of these bonds is more parallel to the film surface in the thermally evaporated film than in the sol-gel film. The data suggest that the method of growth may be used as a controlled variable to select key film characteristics for potential applications.

Advances on transition metal oxides catalysts for formaldehyde oxidation: A review

ABSTRACT This article highlights recent advances in the development of transition metal-based catalysts for formaldehyde oxidation, particularly the enhancement of their catalytic activity for low-temperature oxidation. Various factors that enhance low-temperature activity are reviewed, such as morphology and tunnel structures, synthesis methods, specific surface area, amount and type of active surface oxygen species, oxidation state, and density of active sites are discussed. In addition, catalyst immobilization for practical air purification, reaction mechanism of formaldehyde oxidation, and the reaction parameters affecting the overall efficiency of the reaction are also reviewed.