Applied Surface Science (v.388, #PB)
Editorial Board (ii).
Preface by Marcin Pisarek; Hiroki Habazaki; Aleksander Krupski; Paweł Kulesza; Maria Janik-Czachor (605-607).
The use of renewable energy in the form of methane via electrolytic hydrogen generation using carbon dioxide as the feedstock by Koji Hashimoto; Naokazu Kumagai; Koichi Izumiya; Hiroyuki Takano; Hiroyuki Shinomiya; Yusuke Sasaki; Tetsuya Yoshida; Zenta Kato (608-615).
The history reveals the continuous increase in world energy consumption and carbon emissions. For prevention of intolerable global warming and complete exhaustion of fossil fuels we need complete conversion from fossil fuel consumption to renewable energy. We have been performing the research and development of global carbon dioxide recycling for more than 25 years to supply renewable energy to the world in the form of methane produced by the reaction of carbon dioxide captured from chimney with hydrogen generated electrolytically using electricity generated by renewable energy. We created the cathode and anode for electrolytic hydrogen generation and the catalyst for carbon dioxide methanation by the reaction with hydrogen. The methane formation from renewable energy will be the most convenient and efficient key technology for the use of renewable energy by storage of intermittent and fluctuating electricity generated from renewable energy and by regeneration of stable electricity. Domestic and international cooperation of companies for industrialization is in progress.
Keywords: Renewable energy; Electrolytic hydrogen generation; Carbon dioxide methanation; Electrodes; Catalyst; Fossil fuel exhaustion; Global warming;
Enhancement of oxidative electrocatalytic properties of platinum nanoparticles by supporting onto mixed WO3/ZrO2 matrix by Iwona A. Rutkowska; Anna Wadas; Pawel J. Kulesza (616-623).
Nanostructured mixed metal (W, Zr) oxide matrices (in a form of layered intercalated films of WO3 and ZrO2) are considered here for supporting and activating catalytic platinum nanoparticles toward electrooxidation of ethanol. Remarkable increases of electrocatalytic (voltammetric, chronoamperometric) currents measured in 0.5 mol dm−3 H2SO4 (containing 0.5 mol dm−3 ethanol) have been observed. Comparison has been made to the behavior of methanol and acetaldehyde under analogous conditions. The enhancement effects are interpreted in terms of specific interactions between platinum nanoparticles and the metal oxide species, high acidity of the mixed oxide sites, as well as high population of surface hydroxyl groups and high mobility of protons existing in close vicinity of Pt catalytic sites. The metal oxide nanostructures are expected to interact competitively (via the surface hydroxyl groups) with adsorbates of the undesirable reaction intermediates, including CO, facilitating their desorption (“third body effect”), or even oxidative removal (e.g., of CO to CO2). The fact that the partially reduced tungsten oxide (HxWO3) component is characterized by fast electron transfers coupled to proton displacements tends to improve the overall charge propagation at the electrocatalytic interface.
Keywords: Ethanol oxidation; Catalytic Pt nanoparticles; Nanostructured mixed metal oxide support; Zirconium(IV) oxide; Tungsten(VI) oxide; Methanol and acetaldehyde intermediates;
Enhanced catalytic activity of solid and hollow platinum-cobalt nanoparticles towards reduction of 4-nitrophenol by Jan Krajczewski; Karol Kołątaj; Andrzej Kudelski (624-630).
Display OmittedPrevious investigations of hollow platinum nanoparticles have shown that such nanostructures are more active catalysts than their solid counterparts towards the following electrochemical reactions: reduction of oxygen, evolution of hydrogen, and oxidation of borohydride, methanol and formic acid. In this work we show that synthesised using standard galvanic replacement reaction (with Co templates) hollow platinum nanoparticles exhibit enhanced catalytic activity also towards reduction of 4-nitrophenol by sodium borohydride in water. Unlike in the case of procedures involving hollow platinum catalysts employed so far to carry out this reaction it is not necessary to couple analysed platinum nanoparticles to the surface of an electrode. Simplification of the analyzed reaction may eliminate same experimental errors. We found that the enhanced catalytic activity of hollow Pt nanoparticles is not only connected with generally observed larger surface area of hollow nanostructures, but is also due to the contamination of formed hollow nanostructures with cobalt, from which sacrificial templates used in the synthesis of hollow Pt nanostrustures have been formed. Because using sacrificial templates is a typical method of synthesis of hollow metal nanostructures, formed hollow nanoparticles are probably often contaminated, which may significantly influence their catalytic activity.
Keywords: Platinum nanoparticles; Hollow platinum nanospheres; Pt catalysts; Reduction of 4-nitrophenol;
Nanostructured MnxOy for oxygen reduction reaction (ORR) catalysts by Luisa Delmondo; Gian Paolo Salvador; José Alejandro Muñoz-Tabares; Adriano Sacco; Nadia Garino; Micaela Castellino; Matteo Gerosa; Giulia Massaglia; Angelica Chiodoni; Marzia Quaglio (631-639).
Display OmittedIn the field of fuel cells, oxygen plays a key role as the final electron acceptor. To facilitate its reduction (Oxygen Reduction Reaction—ORR), a proper catalyst is needed and platinum is considered the best one due to its low overpotential for this reaction. By considering the high price of platinum, alternative catalysts are needed and manganese oxides (MnxOy) can be considered promising substitutes.They are inexpensive, environmental friendly and can be obtained into several forms; most of them show significant electro-catalytic performance, even if strategies are needed to increase their efficiency.In particular, by developing light and high-surface area materials and by optimizing the presence of catalytic sites, we can obtain a cathode with improved electro-catalytic performance. In this case, nanofibers and xerogels are two of the most promising nanostructures that can be used in the field of catalysis.In this work, a study of the morphological and catalytic behavior of MnxOy nanofibers and xerogels is proposed. Nanofibers were obtained by electrospinning, while xerogels were prepared by sol-gel and freeze drying techniques.Despite of the different preparation approaches, the obtained nanostructured manganese oxides exhibited similar catalytic performance for the ORR, comparable to those obtained from Pt catalysts.
Keywords: ORR catalysts; Manganese oxides; Nanofibers; Xerogels;
The influence of coating solution and calcination condition on the durability of Ir1-xSnxO2/Ti anodes for oxygen evolution by Zenta Kato; Ryo Kashima; Kohei Tatsumi; Shinnosuke Fukuyama; Koichi Izumiya; Naokazu Kumagai; Koji Hashimoto (640-644).
For oxygen formation without forming chlorine in seawater electrolysis for hydrogen production we have been using the anode consisting of three layers of MnO2-type multiple oxide catalyst, intermediate layer and titanium substrate. The intermediate layer was used for prevention of oxidation of the titanium substrate during anodic polarization for oxygen evolution and was prepared by calcination of butanol solutions of H2IrCl6 and SnCl4 coated on titanium. The protectiveness of Ir1-xSnxO2 layer formed was directly examined using Ir1-xSnxO2/Ti anodes in H2SO4 solution changing the preparation conditions of the layer. When the sum of Ir4+ and Sn4+ was 0.1 M, the highest protectiveness was observed at 0.06 M Sn4+. Although an increase in calcination temperature led to the formation of Ir1-x-ySnxTiyO2 triple oxide with a slightly lower catalytic activity for oxygen evolution, the anode calcined at 450 °C showed the highest protectiveness.
Keywords: Oxygen evolution anode; Seawater electrolysis; Life elongation; Sn-Ir double oxide intermediate layer;
Highly active carbon supported Pd cathode catalysts for direct formic acid fuel cells by A. Mikolajczuk-Zychora; A. Borodzinski; P. Kedzierzawski; B. Mierzwa; M. Mazurkiewicz-Pawlicka; L. Stobinski; E. Ciecierska; A. Zimoch; M. Opałło (645-652).
One of the drawbacks of low-temperature fuel cells is high price of platinum-based catalysts used for the electroreduction of oxygen at the cathode of the fuel cell. The aim of this work is to develop the palladium catalyst that will replace commonly used platinum cathode catalysts. A series of palladium catalysts for oxygen reduction reaction (ORR) were prepared and tested on the cathode of Direct Formic Acid Fuel Cell (DFAFC). Palladium nanoparticles were deposited on the carbon black (Vulcan) and on multiwall carbon nanotubes (MWCNTs) surface by reduction of palladium(II) acetate dissolved in ethanol. Hydrazine was used as a reducing agent. The effect of functionalization of the carbon supports on the catalysts physicochemical properties and the ORR catalytic activity on the cathode of DFAFC was studied. The supports were functionalized by treatment in nitric acid for 4 h at 80 °C. The structure of the prepared catalysts has been characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscope (TEM) and cyclic voltammetry (CV). Hydrophilicity of the catalytic layers was determined by measuring contact angles of water droplets. The performance of the prepared catalysts has been compared with that of the commercial 20 wt.% Pt/C (Premetek) catalyst. The maximum power density obtained for the best palladium catalyst, deposited on the surface of functionalized carbon black, is the same as that for the commercial Pt/C (Premetek). Palladium is cheaper than platinum, therefore the developed cathode catalyst is promising for future applications.
Keywords: Cathode; Palladium; Direct formic acid fuel cells; Electro-reduction of oxygen;
Highly active Ni/Y-doped ZrO2 catalysts for CO2 methanation by H. Takano; Y. Kirihata; K. Izumiya; N. Kumagai; H. Habazaki; K. Hashimoto (653-663).
The catalytic methanation of CO2 was carried out on Ni catalysts supported on Y-doped ZrO2 with various Y3+ concentrations and Ni/(Zr + Y) molar ratio = 1. The catalysts were characterized by X-ray diffraction, scanning transmission electron microscopy, specific surface area, temperature-programmed desorption of CO2, and temperature-programmed reaction. In addition, operando diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFT) was used to identify the adsorbed reaction intermediate. Catalysts supported on Y-doped ZrO2 show higher catalytic activity than the catalyst on Y-free ZrO2 with a monoclinic ZrO2 phase. The catalytic activity is also dependent upon the Y3+ concentration, and the highest activity was obtained for the catalyst with a Y/(Zr + Y) molar ratio of 0.333, which consists mainly of fcc Ni and cubic ZrO2 phase. Y3+ doping into ZrO2 introduces oxygen vacancies, which play an important role in enhancing the catalytic activity. The operando DRIFT study reveals that a CO adsorption intermediate is absent, and bidentate carbonate is an important intermediate for CH4 formation.
Keywords: Methanation of CO2; Supported Ni catalyst; ZrO2; Oxygen vacancy; Power to gas;
TiO2 assisted photo-oxidation of wastewater prior to voltammetric determination of trace metals: Eco-friendly alternative to traditional digestion methods by Beata Lejbt; Natalia Ospina-Alvarez; Krzysztof Miecznikowski; Beata Krasnodębska-Ostręga (664-669).
Voltammetry is a sensitive method for metal determination and one alternative to ICP MS, but its limitation is the influence of the organic matrix on the measurements. To avoid those interferences, wet digestion with H2O2 accelerated with UV irradiation is applied and evaporation of excess of reagents is required. In this study, photolytic oxidation in quartz tubes with anatase was carried out, using as object of study wastewater samples with high amount of organic matter. Cadmium and lead determination was carried out in order to test metal recoveries. Lead recoveries reached c.a 85% for UV digestion with hydrogen peroxide, 98% for digestion with anatase immobilized with polyvinylidene fluoride (N-metylo-2-pirolidon) and c.a 103% for digestion with immobilized anatase (anatase in gum). The results obtained showed the usefulness of TiO2 layer as an oxidation medium. An easy, cheap and eco-friendly digestion method of surfactants without any reagent has been developed, with equal sensitivity but and the same detection limit of traditional digestion methods.
Keywords: Photocatalytic decomposition; Anodic stripping voltammetry; UV digestion; Wet digestion; Polyvinylidene fluoride; Titanium dioxide;
Investigation of the degradation mechanism of catalytic wires during oxidation of ammonia process by Jarosław Pura; Piotr Wieciński; Piotr Kwaśniak; Marta Zwolińska; Halina Garbacz; Joanna Zdunek; Zbigniew Laskowski; Maciej Gierej (670-677).
The most common catalysts for the ammonia oxidation process are 80 μm diameter platinum-rhodium wires knitted or woven into the form of a gauze. In an aggressive environment and under extreme conditions (temperature 800–900 °C, intensive gas flow, high pressure) precious elements are drained from the surface of the wires. Part of this separated material quickly decomposes on the surface in the form of characteristic “cauliflower-shape protrusions”. The rest of the platinum is captured by palladium-nickel catalytic-capture gauzes located beneath.In our investigation we focused on the effects of the degradation of gauzes from one industrial catalytic system. The aim of the study was to compare the degree and the mechanism of degradation of gauzes from a different part of the reactor. The study covered PtRh7 catalytic and PdNi5 catalytic-capture gauzes.X-ray computer microtomography investigation revealed that despite strong differences in morphology, each Pt-Rh wire has a similar specific surface area. This indicates that the oxidation process and morphological changes of the wires occur in a self-regulating balance, resulting in the value of the specific surface area of the catalyst. Microtomography analysis of Pd-Ni wires revealed strong redevelopment of the wires’ surface, which is related to the platinum capture phenomenon.Scanning electron microscope observations also revealed the nanostructure in the cauliflower-shape protrusions and large grains in the wires’ preserved cores. The high temperature in the reactor and the long-term nature of the process do not favor the occurrence of the nanostructure in this type of material. Further and detailed analysis of this phenomena will provide a better understanding of the precious metals etching and deposition processes during oxidation.
Keywords: Platinum; Catalysis; Degradation;
Deposition of copper and sulfate on Au(1 1 1): New insights by B. Madry; K. Wandelt; M. Nowicki (678-683).
Display OmittedThe adsorption of sulfate anions ( S O 4 2 − ) and copper cations on Au(1 1 1) from CuSO4 containing H2SO4 solution was investigated by cyclic voltammetry (CV) and scanning tunneling microscopy (STM). The underpotential deposition from solution results first in the formation of 2/3 monolayer of copper with the well known ( 3 × 3 ) structure of sulfate followed by the completion of the first copper monolayer at lower potentials. Just after formation of 1ML of Cu STM reveals a disordered surface. At more negative potential values, already in the overpotential deposition region, the STM images reflect a ( 3 × 7 ) sulfate structure on terraces of the first pseudomorphic Cu layer, a ( 3 × 3 ) -like structure on terraces of the second uncompleted Cu layer with sulfate anions residing in atomic vacancies, and the known Moiré structure on terraces of the multi-layer Cu deposit. The formation of the ( 3 × 7 ) sulfate structure on pseudomorphic monolayer Cu terraces on Au(1 1 1) is discussed in the context of results obtained for sulfate on bare Au(1 1 1) and Cu(1 1 1) electrodes in H2SO4 solution.
Keywords: Copper; Gold; Sulfate; Solid–liquid interface; Surface structure; Underpotential deposition (UPD); Overpotential deposition (OPD); Cyclic voltammetry (CV); Electrochemical scanning tunneling microscopy (EC-STM);
Optimisation of anatase TiO2 thin film growth on LaAlO3(0 0 1) using pulsed laser deposition by K. Krupski; A.M. Sanchez; A. Krupski; C.F. McConville (684-690).
Optimisation of epitaxial anatase TiO2 thin films grown on LaAlO3(0 0 1) substrates was performed using ultra-high vacuum based pulsed laser deposition (PLD) and studied by in-situ reflection high-energy electron diffraction (RHEED). In addition, ex-situ X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were performed to characterise the bulk properties of these thin films. The deposited TiO2 thin film is demonstrated to have anatase phase and bonded directly to the LaAlO3(0 0 1) substrate. In a separate ultra-high vacuum system low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) measurements were performed and a well-ordered two-domain (1 × 4) and (4 × 1) reconstruction of anatase surface was observed. Analysis of the STM measurements indicates the coexistence of atomic steps of both 2.5 Å and 5.0 Å, confirming the existence of two TiO2 domains. The atomic resolution STEM images reveal that the TiO2/LaAlO3 interface to be terminated with LaO layer and that the anatase-TiO2 reconstruction was found to be stable during the film growth.
Keywords: Anatase; Titanium dioxide; Lanthanum aluminate; Pulsed laser deposition (PLD); Reflection high-energy electron diffraction (RHEED); Low-energy electron diffraction (LEED); X-ray diffraction (XRD); Atomic force microscopy (AFM); Scanning tunneling microscopy (STM); Scanning transmission electron microscopy (STEM); Growth; Thin film growth;
Surface studies of praseodymium by electron spectroscopies by Mirosław Krawczyk; Marcin Pisarek; Wojciech Lisowski; Aleksander Jablonski (691-695).
Electron transport properties in praseodymium (Pr) foil samples were studied by elastic-peak electron spectroscopy (EPES). Prior to EPES measurements, the Pr sample surface was pre-sputtered by Ar ions with ion energy of 2–3 keV. After such treatment, the Pr sample still contained about 10 at.% of residual oxygen in the surface region, as detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses. The inelastic mean free path (IMFP), characterizing electron transport within this region (4 nm-thick), was evaluated from EPES using both Ni and Au standards as a function of energy in the range of 0.5–2 keV. Experimental IMFPs, λ, were approximated by the simple function λ = kE p , where E is energy (in eV), and k = 0.1549 and p = 0.7047 were the fitted parameters. These values were compared with IMFPs for the praseodymium surface in which the presence of oxygen was tentatively neglected, and also with IMFPs resulting from the TPP-2M predictive equation for bulk praseodymium. We found that the measured IMFP values to be only slightly affected by neglect of oxygen in calculations. The fitted function applied here was consistent with the energy dependence of the EPES-measured IMFPs. Additionally, the measured IMFPs were found to be from 2% to 4.2% larger than the predicted IMFPs for praseodymium in the energy range of 500–1000 eV. For electron energies of 1500 eV and 2000 eV, there was an inverse correlation between these values, and then the resulting deviations of −0.4% and −2.7%, respectively, were calculated.
Keywords: Praseodymium; Elastic-peak electron spectroscopy; Electron inelastic mean free path; Surface composition; X-ray photoelectron spectroscopy; Auger electron spectroscopy;
Surface characterization of graphene based materials by M. Pisarek; M. Holdynski; M. Krawczyk; R. Nowakowski; A. Roguska; A. Malolepszy; L. Stobinski; A. Jablonski (696-703).
In the present study, two kind of samples were used: (i) a monolayer graphene film with a thickness of 0.345 nm deposited by the CVD method on Cu foil, (ii) graphene flakes obtained by modified Hummers method and followed by reduction of graphene oxide. The inelastic mean free path (IMFP), characterizing electron transport in graphene/Cu sample and reduced graphene oxide material, which determines the sampling depth of XPS and AES were evaluated from relative Elastic Peak Electron Spectroscopy (EPES) measurements with the Au standard in the energy range 0.5–2 keV. The measured IMFPs were compared with IMFPs resulting from experimental optical data published in the literature for the graphite sample. The EPES IMFP values at 0.5 and 1.5 keV was practically identical to that calculated from optical data for graphite (less than 4% deviation). For energies 1 and 2 keV, the EPES IMFPs for rGO were deviated up to 14% from IMFPs calculated using the optical data by Tanuma et al. . Before EPES measurements all samples were characterized by various techniques like: FE-SEM, AFM, XPS, AES and REELS to visualize the surface morphology/topography and identify the chemical composition.
Keywords: Graphene; Reduced graphene oxide (rGO); Elastic-peak electron spectroscopy (EPES); Electron inelastic mean free path (IMFP); Surface analysis (AES, REELS, XPS);
MnO2-protected silver nanoparticles: New electromagnetic nanoresonators for Raman analysis of surfaces in basis environment by Heman Burhanalden Abdulrahman; Karol Kołątaj; Paweł Lenczewski; Jan Krajczewski; Andrzej Kudelski (704-709).
The first example of the synthesis of Ag nanoparticles protected by a few nanometers thick layer of MnO2 (Ag@MnO2) has been reported. Synthesized Ag@MnO2 nanoparticles effectively locally enhance the electric field of the incident visible radiation, which allows, for example, for a large enhancement of the efficiency of Raman scattering for species located in the close proximity to such nanostructures. It means that Ag@MnO2 nanoparticles may be used as nanoresonators for shell-isolated nanoparticle-enhanced Raman scattering (SHINERS) measurements. The obtained Ag@MnO2 nanoparticles are almost two orders of magnitude more efficient in enhancing Raman signal than previously used for SHINERS measurements in the alkali environment Au@MnO2 nanostructures. Moreover, in comparison to Ag@SiO2 nanoparticles, which are standard silver nanoresonators for SHINERS experiments, Ag@MnO2 nanoparticles are significantly more stable in the basic conditions. Deposition of the MnO2 layer (by the reduction of KMnO4 with by K2C2O4 in an alkaline condition) on hollow silver nanoparticles (h-Ag) has been also analyzed. Hollow silver shells are significantly less stable than the solid Ag nanostructures and are practically entirely destroyed during the process of the MnO2 deposition. However, in this condition, the majority of h-Ag nanoparticles form agglomerates containing about 101 h-Ag items which are connected by MnO2, and after dissolution of the silver auxiliary templates very regular MnO2 sponge nanostructures with the diameter of 150–300 nm are formed.
Keywords: Shell-isolated nanoparticle-enhanced Raman spectroscopy; SHINERS; Surface-enhanced Raman spectroscopy; SERS; Ag@MnO2; MnO2 sponge nanostructures;
The role of oxygen in plasmon-driven transformation of silver nanoparticles by Jan Krajczewski; Karol Kołątaj; Sylwia Parzyszek; Heman Burhanalden Abdulrahman; Andrzej Kudelski (710-715).
Display OmittedPlasmon-driven transformation (PDTr) of silver nanoparticles is a very valuable tool for formation of various anisotropic silver nanostructures. PDTr involves two steps: slow surface dissolution of silver nanoparticles, and redeposition of dissolved silver by the photocatalytic reduction of Ag+ cations. Photocatalytic reduction of Ag+ occurs preferentially at such places of silver nanostructures, at which strong surface plasmons are excited (usually sharp edges, tips). Therefore, during PDTr the inhomogeneity of nanoparticles may increase. Up to now all synthesis of Ag nanoparticles utilizing PDTr have been carried out in the solution containing dissolved oxygen. In this contribution we have shown that when another oxidising agent (e.g., 1,4-benzoquinone) is present in the reaction mixture, the PDTr of silver nanoparticles can be carried out even in the deoxidised solution. Moreover, using oxidising agents other than oxygen allows for some modification of the PDTr process (especially synthesis of smaller Ag nanostructures). Explanation of the observed phenomenon is proposed (involving complete oxidation by the dissolved oxygen of some very small Ag clusters).
Keywords: Silver nanoparticles; Plasmon resonance; Plasmon-driven transformation; Surface-enhanced Raman scattering; SERS;
Properties of ordered titanium templates covered with Au thin films for SERS applications by Katarzyna Grochowska; Katarzyna Siuzdak; Michał Sokołowski; Jakub Karczewski; Mariusz Szkoda; Gerard Śliwiński (716-722).
Currently, roughened metal nanostructures are widely studied as highly sensitive Raman scattering substrates that show application potential in biochemistry, food safety or medical diagnostic. In this work the structural properties and the enhancement effect due to surface enhanced Raman scattering (SERS) of highly ordered nano-patterned titanium templates covered with thin (5–20 nm) gold films are reported. The templates are formed by preparation of a dense structure of TiO2 nanotubes on a flat Ti surface (2 × 2 cm2) and their subsequent etching down to the substrate. SEM images reveal the formation of honeycomb nanostructures with the cavity diameter of 80 nm. Due to the strongly inhomogeneous distribution of the electromagnetic field in the vicinity of the Au film discontinuities the measured average enhancement factor (107–108) is markedly higher than observed for bare Ti templates. The enhancement factor and Raman signal intensity can be optimized by adjusting the process conditions and thickness of the deposited Au layer. Results confirm that the obtained structures can be used in surface enhanced sensing.
Keywords: Anodization; Dimpled Ti templates; Au thin layers; SERS measurements;
Syntheses and properties of several metastable and stable hydrides derived from intermetallic compounds under high hydrogen pressure by S.M. Filipek; V. Paul-Boncour; R.S. Liu; I. Jacob; T. Tsutaoka; A. Budziak; A. Morawski; H. Sugiura; P. Zachariasz; K. Dybko; R. Diduszko (723-730).
Brief summary of our former work on high hydrogen pressure syntheses of novel hydrides and studies of their properties is supplemented with new results. Syntheses and properties of a number of hydrides (unstable, metastable or stable in ambient conditions) derived under high hydrogen pressure from intermetallic compounds, like MeT2, MeNi5, Me7T3, Y6Mn23 and YMn12 (where Me = zirconium, yttrium or rare earth; T = transition metal) are presented. Stabilization of ZrFe2H4 due to surface phenomena was revealed. Unusual role of manganese in hydride forming processes is pointed out. Hydrogen induced phase transitions, suppression of magnetism, antiferromagnetic-ferromagnetic and metal-insulator or semimetal-metal transitions are described. Equations of state (EOS) of hydrides submitted to hydrostatic pressures up to 30 GPa are presented and discussed.
Keywords: Hydrogen storage; Intermetallic alloys; High pressure; Hydrides; Phase transitions; Surface phenomena;
Characterization of optical and microstructural properties of semitransparent TiO2/Ti/glass interference decorative coatings by L. Skowronski; A.A. Wachowiak; A. Grabowski (731-740).
This paper presents a study of the optical properties and the microstructure of semitransparent interference TiO2/Ti/glass systems obtained by gas injection magnetron sputtering (GIMS). The samples are examined by means of spectroscopic ellipsometry, spectrophotometry and atomic force microscopy. The investigation is complemented by colorimetric measurements. Optical constants of titanium and titanium dioxide layers are determined and carefully studied. An influence of the deposition time on the thickness of metallic and dielectric films has been found. The thickness of Ti films ranges from 12 nm to 73 nm, while that of TiO2 films varies from 11 nm to 43 nm. This thickness directly determines the color of a sample from gold to blue, respectively.
Keywords: Decorative coatings; Interference systems; Magnetron sputtering; GIMS; Titanium dioxide; CIE Lab color space;
Terahertz characterization of Y2O3-added AlN ceramics by Seung Beom Kang; Dong Chul Chung; Sung-Jin Kim; Jun-Ki Chung; Sang-Yeup Park; Ki-Chul Kim; Min Hwan Kwak (741-745).
Terahertz optical and dielectric properties of AlN ceramics fabricated by hot pressed sintering are investigated by THz time-domain spectroscopy in the frequency range of 0.2–3.5 THz. The measured properties of the pure AlN ceramic are compared with those of Y2O3-added AlN ceramic. Two prominent resonance modes, which are essentially responsible for the dielectric properties of the Y2O3-added AlN in terahertz regime, are characterized at ω TO1 /(2π) = 2.76 THz (92 cm−1) and ω TO2 /(2π) = 18.2 THz (605 cm−1) and are well described by the pseudo-harmonic oscillator model through theoretical fitting. The resonance ω TO1 at 2.76 THz is proposed to be due to the formation of a YAG (Y3Al5O12) secondary phase in Y2O3-added AlN ceramic. From the experimental results, good correlation is observed between the prominent peak of YAG secondary phase at 2.76 THz and thermal conductivity. Additionally, there is a high correlation between densification and refractive index of AlN ceramics fabricated by hot pressed sintering.
Keywords: THz time-domain spectroscopy; AlN; Thermal conductivity; Densification;
Mesoporous film of WO3–the “sunlight” assisted decomposition of surfactant in wastewater for voltammetric determination of Pb by Beata Krasnodębska-Ostręga; Agnieszka Bielecka; Ewa Biaduń; Krzysztof Miecznikowski (746-752).
In this paper we present the application of “sunlight” assisted digestion in the presence of WO3 to the decomposition of dissolved organic matter, using the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant (1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton™X-114) in natural water samples, prior to the determination of traces residues of lead by stripping voltammetry methods. The results of the study showed firstly that the preparation of reproducible WO3 layers characterized by high mechanical and chemical resistance was possible, and secondly that it was also possible to obtain a high efficiency of decomposition, equal in efficiency to that of the reference method, which was the hydrogen peroxide oxidation assisted by UV, with evaporation nearly to dryness. The developed procedure is suggested to be a no-reagents method for the decomposition of added SDS, leading to 100% recovery of added Pb (II). The anodic stripping voltammetric curves recorded in solution after 4 h irradiation with UV assisted by WO3 were repeatable and increased linearly with standard additions, but the data finally obtained were incorrect. The curves recorded in solution after “sunlight” assisted digestion in the presence of WO3 were repeatable, and increased linearly with an increasing of concentration of standard additions (100% recovery of Pb). In the case of a nonionic surfactant, the decomposition time is at least 6 h. The advantage of the proposed method is the fact that the digestion process does not need the addition of any chemicals for the complete decomposition of organic matter.
Keywords: Mesoporous WO3; Photocatalysts; Stripping voltammetry; UV digestion; Sunlight decomposition; Surfactants;
Enhanced photoelectrochemical performance of inorganic–organic hybrid consisting of BiVO4 and PEDOT:PSS by K. Trzciński; M. Szkoda; K. Siuzdak; M. Sawczak; A. Lisowska-Oleksiak (753-761).
The PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) was electrodeposited on a thin layer of bismuth vanadate (BiVO4) prepared using the pulsed laser deposition technique onto FTO. The inorganic–organic junction was characterized by Raman spectroscopy, UV–vis spectroscopy and scanning electron microscopy. Chronoamperometry curves, recorded under simulated solar light illumination, were performed to determine generated photocurrent during water and hydroquinone oxidation at the electrode surface. Experiments were performed for three types of electrode materials: (i) FTO/BiVO4, (ii) FTO/PEDOT:PSS and (iii) FTO/BiVO4/PEDOT:PSS in aqueous electrolyte. Almost 5 times higher photocurrent in electrolyte containing hole scavenger was generated after modification of BiVO4 photoanode with electrodeposited polymer. It is noteworthy that anodic photocurrent was stable even after 4 h of illumination. Cyclic voltammetry curves of FTO/BiVO4/PEDOT:PSS recorded before and after experiments performed under electrode illumination indicated that the organic part in tested junction is photo-corrosion resistant.
Keywords: Photoanode; BiVO4; PEDOT:PSS; Photocurrent;
How important are scaffolds and their surface properties in regenerative medicine by J. Idaszek; E. Kijeńska; M. Łojkowski; W. Swieszkowski (762-774).
The ability of cells to sense various cues present within their natural habitat gives a tremendous opportunity to steer their fate in vitro within artificial matrices (scaffolds). However, the variety of signals and their chemical and physical origin makes engineering of the scaffolds quite challenging and requires careful design in order to obtained the desired outcome. Herein, we discuss the effect of architecture and surface of scaffolds fabricated by means of additive manufacturing and electrospinning on cell retention, spreading, proliferation and differentiation. Additionally, we present some of the reported surface and bulk modifications of the scaffolds, which positively affected cell performance. Finally, in the last part we discuss application of multicellular spheroids as a useful tool to study cell performance within three-dimensional and porous structures.
Keywords: Scaffolds; Additive manufacturing; Electrospinning; Architecture; Surface properties; Tissue engineering;
Improvement of the bio-functional properties of TiO2 nanotubes by A. Roguska; M. Pisarek; A. Belcarz; L. Marcon; M. Holdynski; M. Andrzejczuk; M. Janik-Czachor (775-785).
Display OmittedTitanium oxide nanotubes with diameters from ca. 40–120 nm fabricated by the anodic oxidation of Ti at a constant voltage (10–28 V) were investigated to identify factors improving their bio-functional properties. Prepared substrates were subsequently annealed at 450 °C and 650 °C to obtain nanotubes having a crystalline structure, and were then examined by SEM, XRD, XPS, BET and contact angle measurement techniques. The thermally stabilized surfaces were subjected to bidirectional functionalization: by deposition of a thin layer of Ca-P and by loading with silver nanoparticles. Three factors were found to promote the proliferation of osteoblast (U2OS) cells: a larger nanotube diameter, a higher annealing temperature, and the presence of a thin Ca-P layer. Differentiation of these cells (by ALP test) was stimulated by a higher (650 °C) nanotube annealing temperature, but not by a thin Ca-P layer. The TiO2 nanotubes-modified samples exhibited noticeable antibacterial properties. Moreover, the additional deposition of Ag nanoparticles almost completely inhibited the survivability of S. epidermidis cells beyond 3 h of contact. In conclusion, TiO2 nanotubes-modified surfaces exhibit distinct bone forming ability and significant antibacterial properties, and can be easily functionalized by a thin Ca-P layer or nano-Ag deposition for further improvement of the above functionalities.
Keywords: Titanium oxide nanotubes (TiO2 NT); Surface characterization methods; Bone forming ability; Bioactivity; Antibacterial properties;
Electrodeposited non-stoichiometric tungstic acid for electrochromic applications: film growth modes, crystal structure, redox behavior and stability by Leonid V. Pugolovkin; Olga V. Cherstiouk; Lyudmila M. Plyasova; Irina Yu. Molina; Tatyana Yu. Kardash; Olga A. Stonkus; Dmitriy A. Yatsenko; Vasily V. Kaichev; Galina A. Tsirlina (786-793).
Bath composition for cathodic electrodeposition of non-stoichiometric hydrated tungstic acid with high electrochromic efficiency is optimized with account for selective electroreduction of certain isopolytungstates. XRD data for thin electrodeposited films and chemically synthesized bulk tungstic acid dihydrate are compared in the context of reversible oxidation and reduction in hydrogen atmosphere, in presence of Pt catalyst. XPS and ТЕМ techniques are attracted to understand the nature of reversible and less reversible transformations of films in the course of their storage and operation.
Keywords: Oxide electrodeposition; Electrochromic films; Tungstic acid; Non-stoichiometry;
Electrodeposition of Al-Ta alloys in NaCl-KCl-AlCl3 molten salt containing TaCl5 by Kazuki Sato; Hisayoshi Matsushima; Mikito Ueda (794-798).
To form Al-Ta alloys for high temperature oxidation resistance components, molten salt electrolysis was carried out in an AlCl3-NaCl-KCl melt containing TaCl5 at 423 K. The voltammogram showed two cathodic waves at 0.45 V and 0.7 V vs. Al/Al(III), which may correspond to reduction from Ta(V) to Ta(III) and from Ta(III) to tantalum metal, respectively. Electrodeposits of Al and Ta were obtained in the range from −0.05 to 0.3 V and the highest concentration of Ta in the electrodeposit was 72 at% at 0.3 V. With increasing Ta content in the alloy, the morphology of the electrodeposits became powdery and the particle size smaller.
The effect of foil purity on morphology of anodized nanoporous ZrO2 by Ewa Wierzbicka; Karolina Syrek; Grzegorz D. Sulka; Marcin Pisarek; Maria Janik-Czachor (799-804).
Display OmittedA two-step electrochemical formation of nanoporous zirconium oxide layers on different zirconium foils (purity 99.2% and 99.8%) was investigated. Anodizations were carried out at 20 V in an electrolyte composed of 1 M (NH4)2SO4 and 0.15 M NH4F. It was found that the thickness of grown oxide layer, and consequently, the rate of oxide formation depend slightly on the Zr substrate purity. The pore nucleation and anodization process occur easier in the presence of higher concentration of impurities. From top view SEM images, the structural parameters of oxide layers such as pore diameter, interpore distance, pore density, wall thickness and porosity of anodic oxide layers were estimated for both types of used substrates. On the other hand, cell size, intercell distance and cell density were evaluated from the bottom side of anodic oxide layers. A special emphasis was put on the qualitative analysis of hexagonal arrangement of nanopores and cells. The nanopore and cells arrangements in formed oxides were evaluated using various approaches based on Delaunay triangulations, angular distribution functions (ADFs) and pair distribution functions (PDFs). These results were supported by calculations of percentage of defective pores and cells for both types of used Zr substrates. The use of low purity Zr for anodizing does not affect drastically the morphology of formed nanoporous zirconia and offers a promising perspective to reduce production costs and increase availability of this material.
Keywords: Zirconium oxide; Anodization; Metal purity; Morphology; Nanopores;
Analysis of electrodeposition parameters influence on cobalt deposit roughness by Sylwia Banbur-Pawlowska; Krzysztof Mech; Remigiusz Kowalik; Piotr Zabinski (805-808).
Over the last years an increased interest has been seen in the electrodeposition of cobalt and cobalt alloys. An essential challenge in the electrodeposition of cobalt is to control the structure and morphology which, in turn, depends on the preparation conditions. The work presents an assessment of the influence of parameters of cobalt deposition in potentiostatic conditions on the structure and morphology of the obtained deposits surface. The level of development of electrocatalytically deposited cobalt layers was examined through microscope methods with the use of the atomic force microscope. Additionally, the samples structure was analysed using X-radiation.The conducted tests allow drawing the following conclusions. The level of surface development does not depend on the applied potential at which deposition of cobalt is carried out. Deposition at low potentials result in creating, on the surface the mixture of metallic cobalt and hydroxides with high level of surface development. High concentration of cobalt ions in the solution result in obtaining close values of the surface development level irrespective of the applied deposition potential.
Keywords: Electrodeposition; Surface roughness; Cobalt;
Electrodeposition of NiPd alloy from aqueous chloride electrolytes by K. Mech; M Wróbel; M Wojnicki; J. Mech-Piskorz; P. Żabiński; R. Kowalik (809-816).
Presented results describing properties of alloys deposited at potentiostatic conditions in Ni2+ – Pd2+ – Cl− – H2O system. Electrolysis parameters were defined based on results of thermodynamic analysis as well as voltammetry coupled with electrochemical quartz crystal microbalance (EQCM). Influence of electrode potential and electrolyte components concentration on alloy composition, morphology and its structure was investigated. Alloys were deposited at different Ni(II) and Pd(II) complexes concentrations. Results indicated possibilities of electrochemical synthesis of alloys of wide composition range. Deposits structure as well as crystallites size were discussed based on results of XRD measurements. Alloys composition was determined with the use of energy dispersive spectroscopy (EDS). Morphology of alloys was characterized with the use of scanning electron microscopy (SEM).
Keywords: Ni-Pd alloy; Electrodeposition; Voltammetry; Chloride electrolytes;
Analysis of tellurium thin films electrodeposition from acidic citric bath by Remigiusz Kowalik; Dawid Kutyła; Krzysztof Mech; Piotr Żabiński (817-824).
This work presents the description of the electrochemical process of formation thin tellurium layers from citrate acidic solution. The suggested methodology consists in the preparation of stable acidic baths with high content of tellurium, and with the addition of citrate acid. In order to analyse the mechanism of the process of tellurium deposition, the electroanalytical tests were conducted. The tests of cyclic voltammetry and hydrodynamic ones were performed with the use of polycrystalline gold disk electrode. The range of potentials in which deposition of tellurium in direct four-electron process is possible was determined as well as the reduction of deposited Te° to Te2− and its re-deposition as a result of the comproportionation reaction. On the basis of the obtained results, the deposition of tellurium was conducted by the potentiostatic method. The influence of a deposition potential and a concentration of TeO2 in the solution on the rate of tellurium coatings deposition was examined. The presence of tellurium was confirmed by X-ray spectrofluorometry and electron probe microanalysis. In order to determine the phase composition and the morphology, the obtained coatings were analysed with the use of x-ray diffraction and scanning electron microscopy.