Function Of Thermal Treatment Research Articles

Preliminary spectroscopic investigation of a potential Mars analog site: Lake Bagno dell’Acqua, Pantelleria, Italy

In this study, we characterize the mineralogy and microbiology of a suite of samples from the Bagno dell’Acqua alkaline (pH ≥ 9) lake in Pantelleria, Italy. The aim of the present characterization is the assessment of the lake as a Martian analog site. Nineteen samples were characterized by a combination of VNIR reflectance spectroscopy, micro-Raman (μ-Raman) spectroscopy, and fluorescence microscopy. In addition, DNA extraction was performed on three selected samples to identify the bacteria phyla and to quantify their abundance. The samples were collected as push cores inside the lake and as loose sediments taken along the eastern and southeastern lake's shore. The samples underwent three thermal cycles (between 343 K and 473 K) to remove excess water and organic matter. The VNIR spectra were measured on each sample after each thermal cycle to check the variation of the spectral features as a function of thermal treatment. The mineralogical content of our push core samples is dominated by the presence of Mg-smectite clays always associated with the remanence of K-feldspars and Ca-carbonates while in the sediments we observe also additional minor phases like pyroxene (aegirine NaFe3+Si2O6), hematite (Fe2O3), anatase (TiO2), and volcanic glass. Two organic phases were detected by μ-Raman spectroscopy. One phase was attributable to carotenoids, in line with the high abundance of Bacterial Phyla that can synthesize these molecules. The second phase appeared to be visually indistinguishable from the inorganic matrix and is therefore attributed to EPS (Extracellular Polymeric Substances) forming a biofilm and extensively observed by fluorescent microscopy. The peculiar chemistry of the waters, the presence of Mg-smectite in the sediments of Lake Bagno dell’Acqua associated with Ca-carbonates and sediments derived by biological activity makes Lake Bagno dell’Acqua a very interesting and promising Martian analog site.

Hollow TiO2 Supports for Enhanced Acidic Oxygen Evolution Activity

The usage of scarce and expensive iridium as a catalyst for the acidic oxygen evolution reaction (OER) represents a significant barrier to up-scaling the deployment of proton exchange membrane water electrolysers (PEM-WEs). Accordingly, strategies such as nanostructuring catalysts to increase the electrochemical surface area (e.g. nanoparticles, single-atom catalysts, nanoclusters) as well as investigating mixed metal alloys and oxides (e.g. perovskites, pyrochlores) have been developed with promising half-cell performances. One further approach that has recently gained attention is the deployment of catalyst-supports whereby a high surface area support is used to scaffold the dispersed iridium catalyst.1 Analogous to the selection of a catalyst, the catalyst support must withstand the highly corrosive and oxidising conditions of a PEM-WE anode. Thus, metal oxides such as titanium dioxide are commonly deployed as catalyst-supports for acidic OER. The catalyst-support moiety must also be sufficiently conductive when integrated into the PEM-WE catalyst layers. Otherwise, the cell voltages required to generate sufficient activity will render the device impractical. Accordingly, strategies such as doping, or the addition of conductive layers between the catalyst and support have been investigated.2 In this study we investigate a unique support morphology that affords promising OER activity and stability in acidic electrolyte with high iridium mass activities. Specifically, we deploy a hollow TiO2 catalyst support,3 coated with a Au/Pd interlayer to provide electrical conductivity. The OER activity and stability is initially screened in a rotating disk electrode (RDE) configuration as a function of thermal treatments (reducing vs oxidising) as well as with at various Au/Pd (1 – 5 wt%) and Ir loadings (35 – 50 wt%). Our highest performing catalyst have a mass activity of around 480 A/gIr at 1.60 V vs RHE. The catalysts are subsequently investigated in a membrane electrode assembly (MEA) and subject to 10k accelerated stress test stability measurements. To understand the role of the support morphology, Au/Pd interlayer and iridium loadings on electrochemical performance, we also characterise the synthesised catalysts by (scanning) transmission electron microscopy (STEM/TEM), X-ray diffraction (XRD), X-ray photoelectron microscopy (XPS) and electrical conductivity measurements. Collectively, we report the critical role of the Au/Pd interlayer to enable such high electrochemical performance. We also show that the hollow structure of the TiO2 support may be enhancing mass transport in the catalyst layers. References 1 A. S. Pushkarev, I. V Pushkareva and D. G. Bessarabov, Energy & Fuels, 2022, 36, 6631–6625.2 Y. N. Regmi, E. Tzanetopoulos, G. Zeng, X. Peng, D. I. Kushner, T. A. Kistler, L. A. King and N. Danilovic, ACS Catal., 2020, 10, 13125–13135.3 U. S. Jonnalagadda, X. Su and J. J. Kwan, Ultrason. Sonochem., 2021, 73, 105530.

Investigating the Trade‐off between Optical and Mechanical Properties during Constrained Sintering of Mesomorphic Ceramic Films

AbstractRobust, transparent, and birefringent inorganic films are demanded for polarization control of high‐power lasers. While single crystals or films obtained via glancing angle deposition exhibit desirable optical properties and laser damage resistance, these methods are limited by cost and scalability. Mesomorphic ceramics as inorganic solids with liquid crystalline superstructure offer appealing transparency and birefringence but lack mechanical robustness due to their high porosity. Here, the effect of sintering on optical and mechanical properties of mesomorphic ceramics is evaluated. Films prepared by blade coating are sintered under varying conditions. Constrained sintering accomplished crystallite growth, densification, and morphological changes including necking as well as cracking while preserving the crystallographic orientation. The extent of sintering as a function of thermal treatment is quantified by morphology, surface area loss, and crystallite growth. Moreover, activation energies for surface diffusion and grain growth are estimated by surface area analysis and X‐ray diffraction peak narrowing, respectively. After sintering, birefringence decreases while Young's modulus and hardness improve as the film densifies. Upon partial sintering, mesomorphic ceramics retain transparency, high birefringence, and enhanced modulus. Laser‐induced damage threshold is measured as well. The reported results represent an important step toward the assembly and sintering of robust waveplates with high laser damage resistance.

Revisiting γ-alumina surface models through the topotactic transformation of boehmite surfaces

The rational understanding of γ-alumina (γ-Al2O3) supported catalysts requires an ever more improved atomic scale determination of the support’s surface properties. By using density functional theory (DFT) calculations, we show how the structural and energetic surface properties of alumina crystallites intrinsically depend on its synthesis pathway. Considering the case study of the topotactic transformation of boehmite (γ-AlOOH) into γ-Al2O3 taking place during calcination, we propose a methodology to mimic this pathway by reconstructing relevant slabs of boehmite into γ-alumina slabs following 3 steps: dehydration, contraction/translation and Al migration into spinel or non-spinel sites. On the one hand, we confirm the reliability of some earlier 100, 110 and 111 surface structures determined by standard bulk cleavage approach. Moreover, we find new γ-alumina surfaces harboring Brønsted acid sites (BAS) and Lewis acid sites (LAS) with specific local structures. More strikingly, we find that the basal 110b surface of alumina inherited from the (010) basal surface of boehmite, exhibits a larger number of isolated µ2-OH groups than the lateral 110l surface. For the lateral 110l (respectively 111) orientation, four (respectively three) thermodynamically competing surfaces are identified, including models earlier proposed. These results are induced by finite size and morphology effects during the topotactic transformation of boehmite crystallites. Thanks to a thorough comparative analysis of morphology and nature of BAS and LAS as a function of thermal treatment and water pressure for each surface, we identify coherent chemical families of surfaces across the main crystallographic orientations. These features open the door to a better differentiation of the reactivity of the basal alumina surfaces from the lateral ones.

Cement Substitution in High-Temperature Concrete

An alternative binder to calcium aluminate cement (CAC) was prepared by the sol-gel method. Chemically pure systems such as tetraethylorthosilicate (SiC8H20O4) and nonahydrate of alumina nitrate (Al(NO3)3·9H2O) were used as major raw materials. The manufacturing process of binder via solution is mentioned, and transitions in binder structure as a function of thermal treatment in the range between 85 and 1400 °C are described. Finally, binder efficiency was verified by its application in high-temperature concrete instead of calcium aluminate cement (CAC). Newly developed sol-gel binder was characterized by XRFS quantitative analyses, XRD diffraction, STA-DTA and TG analyses and the BET method. Samples of concrete which were based on natural bauxite raw material showed cold compressive strength of 42 MPa compared to the same material where a conventional CAC was applied, and samples reached cold compressive strength of 44 MPa.

Influence of annealing temperature on the existence of polar domain in uniaxially stretched polyvinylidene-co-hexafluoropropylene for energy harvesting applications

The structural and electroactive properties of the as-prepared random copolymer polyvinylidene-co-hexafluoropropylene thin film are explored as a function of thermal treatment at various temperature regions. The thermal treatment of the polymer thin film not only changes the structural conformations that is very natural but establishes a polar domain in the non-polar α-phase. Here, we discover an anomalous temperature-dependent crossover behavior from the non-polar α-phase to an appreciable enhancement in ferroelectric and piezoelectric responses. The maximum unipolar strain (Smax=−5.01%), an ultrahigh value of normalized piezoelectric coefficient (d33∗=−556pm/V), high electromechanical coupling factor (Kp=0.78) factor including the high dielectric constant (ϵ′=23at100Hz) at a relatively low electric field of 900 kV/cm may, therefore, be an effect of the established polar domain for the sample annealed at 105 °C. The direct piezoelectric charge coefficient (d33), a key factor for the performance of a prepared polymer thin film system as an energy harvester, lies in the range of −10±2pC/N. Also, the annealed sample exhibited a persistent polarization after several cumulative cycles of applied stress.

Characterization of Thermally Treated Gas-Atomized Al 5056 Powder.

Aluminum 5056 is a work-hardenable alloy known for its corrosion resistance with new applications in additive manufacturing. A good understanding of the secondary phases in Al 5056 powders is important for understanding the properties of the final parts. In this study, the effects of different thermal treatments on the microstructure of Al 5056 powder were studied. Thermodynamic models were used to guide the interpretation of the microstructure as a function of thermal treatment, providing insight into the stability of different possible phases present in the alloy. Through the use of transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS), combined with thermodynamic modeling, a greater understanding of the internal microstructure of Al 5056 powder has been achieved in both the as-atomized and thermally treated conditions. Evidence of natural aging within these powders was observed, which speaks to the shelf-life of these powders and the importance of proper treatment and storage to maintain consistent results.

Insights on the mechanism of solid state reaction between TiO2 and BaCO3 to produce BaTiO3 powders: The role of calcination, milling, and mixing solvent

Barium titanate (BaTiO3) is well-known for its variety of macroscopic properties, however, the mechanism of formation of this oxide in microscale remains poorly understood. We prepared the BaTiO3 nanoparticles and studied them as a function of milling time and temperature. A systematic study was performed to understand the reaction mechanism of undissociated and dissociated 2-propanol molecules on TiO2 and BaCO3 particles. Structural evolution and thermal decomposition of surface particles were carried out and studied by X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy analysis. Structural parameters refined by Rietveld analysis using X-ray diffraction data revealed a tetragonal structure with P4/mm space group, which was due to the dependence of functional groups on the milling time and thermal treatment. The divergence of tetragonality as a function of thermal treatment was identified for particles of size <400 nm, which probably happened due to surface defects which decreased in low temperature of about 1000 °C. Particle sizes precursors decreased as a function of the milling time from 18 μm (2 h milling) to 1.2 μm (24 h of milling). While by increasing the thermal treatment of samples from 1000 °C to 1100 °C the particles size increased, respectively, 0.24 μm and 0.36 μm. The effect of the particle size of TiO2 plays an important role in the reaction kinetics of the formation of BaTiO3. Our results suggest that the reaction proceeds through a mechanism in which the intermediate processes of TiO2, BaCO3 and dissociation of BaCO3 are trapped by the dissociated and undissociated 2-propanol molecules, which resulted in depletion of 2-propanol-related functional groups in the BaTiO3 particle surface at higher temperature.

Oxygen dissolution and surface oxide reconstructions on Nb(100)

The ever-present native oxide layer on niobium plays a fundamental role in the performance of Nb superconducting radio frequency (SRF) cavities for particle accelerators and light sources. Using Nb(111) and Nb(100) as model systems, oxygen dissolution and surface structural evolution as a function of thermal treatments in ultrahigh vacuum (UHV) were studied using combined Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM), providing novel, real space information regarding the complex evolution of the Nb surface oxide. The surface crystallographic orientation was shown to influence oxide surface structure; Nb(111) displayed disordered surface oxide domains while Nb(100) was comprised of well-ordered, (n × 1)-O domains. The temperature-dependent dissolution of the native oxide layer on Nb(100) was characterized to ascertain the energetics for oxygen dissolution, and evolution of the surface oxide superlattice structure following thermal annealing was observed with STM. By understanding the kinetic behavior of oxygen dissolution during thermal annealing and subsequent structural evolution of the Nb(n × 1)-O superlattice on Nb(100), a more thorough understanding of the complex interactions driving chemical composition and cavity surface structure under Nb SRF cavity processing and operating conditions may be understood.

Microstructure evolution and thermal properties of an additively manufactured, solution treatable AlSi10Mg part

Because of rapid solidification involved in the laser or e-beam based additive manufacturing (AM) process, solution treatable metallic parts made by these methods usually possess a unique nonequilibrium microstructure which changes significantly during subsequent thermal treatment. Such evolution alters the size, morphology, length scale, and distribution of microstructural features and has a substantial impact on thermal properties and possibly on electrical properties as well. This study focuses on effects of microstructural evolution on thermal properties of an additively manufactured AlSi10Mg part. The changes of thermal properties such as thermal expansion, heat capacity, thermal diffusivity, and thermal conductivity as a function of thermal treatment are reported. The results show that the formation of supersaturated primary α aluminum and unique cellular structure imparted by fast solidification in the AM process are the major cause for the low thermal diffusivity and low thermal conductivity observed in this solution treatable, as-built part. A correlation between microstructural evolution and changes in thermal properties is established. Advantages and tailoring of the thermal properties of additively built parts are discussed. Implications of these results are important for other additively manufactured components based on popular solution treatable alloys.

The impact of thermal treatment and cooling methods on municipal solid waste incineration bottom ash with an emphasis on Cl

ABSTRACTMunicipal solid waste incineration (MSWI) bottom-ash products possess qualifications to be utilized in cement production. However, the instant use of bottom ash is inhibited by a number of factors, among which the chlorine (Cl) content is always strictly restricted. In this paper, the unquenched MSWI bottom ash was used as the experimental substance, and the influences of thermal treatment and cooling methods on the content and existence of Cl in the ash residues were investigated. The characterization of the MSWI bottom-ash samples examined by utilizing X-ray diffraction, optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy. The experimental results show that as a function of thermal treatment, the reduction rate of Cl is slight below 15.0%, which is relatively low compared with water washing process. Different cooling methods had impacts on the existing forms of Cl. It was understood that most of Cl existed in the glass phase if the bottom ash was air cooled. Contrarily in case of water-quenched bottom ash, Cl could also be accumulated in the newly-formed quench products as chloride salts or hydrate substances such as Friedel's salt.

A novel approach to study the isothermal and non-isothermal crystallization kinetics of Poly(Ethylene Terephthalate) by Raman spectroscopy

This paper focuses on the study of the crystallization kinetics of an initially quasi-amorphous Poly(Ethylene Terephthalate) (PET) during controlled heating treatments using Raman Spectroscopy. Characteristic vibrational bands of both crystalline and amorphous phases are then investigated in terms of wavenumber values, full widths at half maximum and integrated intensities variations which led to the establishment of a more accurate crystallinity ratio criterion than the one obtained by standard differential scanning calorimetry (DSC) analysis too much dependent on the low polymer thermal conductivity. Applying this last criterion, isothermal and non-isothermal crystallization kinetics were investigated following the Avrami’s and Ozawa’s theories in order to identify the germination and growth modes of the triclinic crystals of PET as a function of thermal treatment. Moreover, all the specific microstructural transitions such as cold crystallization, crystallization from the melt, melting and glass transition are detected and characterized. Similar thermal behaviors were obtained from Raman results and conventional differential scanning calorimetry measurements.

Silver-functionalized methyl-silica hybrid materials as antibacterial coatings on surgical-grade stainless steel

Development of new materials enriched with noble metal ions, such as silver, cobalt or copper, is of great interest in the field of commercial and medical products due to its action against fungus and bacteria. Although a large number of products are chemically active against microorganisms, they are usually limited to fabrics for medical bandages and sportswear in order to avoid, respectively, infections and odors. On the other hand, sol-gel technology becomes the preparation of hybrid materials possible with introduction of different components, as inorganic salts or organic additives within its structure bringing up the possibility to develop functional materials for different purposes. In this work, the development of an antibacterial coating for metallic substrates is presented. The coating consists in a hybrid organic-inorganic sol-gel material doped with silver. The relation between the structure of the hybrid matrix, aggregation state of silver ions, and biocide behavior is analyzed as a function of the densifying thermal treatment. Sol-gel materials were synthesized through hydrolytic condensation, in acidic conditions, of tetraethoxysilane (TEOS) and methyl-triethoxysilane (MTES). Silica nanoparticles were added in order to give a mechanical reinforcement and silver nitrate as the supplier of Ag+ ions. Coatings were deposited on 316L stainless steel and microscope glass slides by the dip-coating process at a constant withdrawal rate and densified at 50, 150 and 450 °C. X-ray photoelectron spectroscopy, small angle X-ray spectroscopy and electrochemical impedance spectroscopy were used as characterization techniques in order to elucidate silver aggregation and its influence on the structural evolution of the hybrid matrix, as a function of the thermal treatment. At the same time, the biocide behavior, as a function of silver state, particles size and thermal treatment, was studied by inhibitory halo identification on Escherichia-coli cultures in agar diffusion tests.

Synthesis of Non-PGM ORR Catalysts: Control of Chemical, Morphological and Catalytic Properties

Development of non-platinum catalysts for both the anode [1] and cathode [2] attracts significant attention from researchers around the globe. Catalysts consisting of transition metal, nitrogen and carbon (M-N-C) where M=Fe, Co, Ni etc)framework possess reasonable stability and activity in both acidic and alkaline media. The use of inexpensive organic precursors doped with low molecular weight metal salts is proposed in the present research to provide a high surface area framework consisting of C-N decorated with M species. All catalysts presented in this work were synthesized using a modified sacrificial silica support method which has been widely adopted in our research group [4]. Appropriate amounts of metal precursor (iron nitrate or cobalt nitrate) and nitrogen-containing, precursors (e.g. polyethyleneimine (PEI)) were deposited on the surface of fumed silica (surface area ~380 m-2 g-1) by Mechanochemical approach. The composite material was pyrolyzed in a nitrogen atmosphere at various temperatures, to form the M-N-C-SiO2framework. The pyrolysis conditions were determined from a MS-TGA analysis, where MS was used to identify the precursor’s decomposition products as a function of thermal treatment. After heat treatment, the fumed silica was removed by etching in HF acid and washed appropriately, revealing a high surface area M-N-C matrix The catalysts were comprehensively characterized by BET, SEM, TEM, XRD and XPS. Catalytic activity for ORR was measured in acidic media (0.5M H2SO4) using the RRDE method and fuel cell test. Figure 1. Mechanochemical synthesis The broad XRD peak for Fe indicates small metallic iron particles exist on the order of several nanometers (Fig. 1). It can be assumed that the homogeneous distribution of precursors on the high surface of fumed silica prevents metal particles from agglomeration. Analysis of material morphology by SEM reveals that the Fe-DAAPyr catalyst yields a highly porous surface structure. BET analysis of the adsorption isotherm reveals a surface area of ~700m-2 g-1. Synthesized materials were found to be active in ORR in both RRDE and MEA fuel cell tests conditions. We would like to acknowledge funding support from DOE-EERE Fuel Cell Technology Program: “Development of Novel Non Pt Group Metal Electrocatalysts for PEM Fuel Cell Applications” (S. Mukerjee, NEU, PI).

Characterisation of microstructure and creep predictions of alloy IN740 for ultrasupercritical power plants

In the context of ultrasupercritical power plants, Ni base alloys are prime candidate materials for long term, high temperature applications, such as boilers, operating at temperatures and pressures as high as 750°C and 35 MPa. This necessitates the investigation of their microstructural evolution as a function of thermal treatment and simulated service conditions out to longer times at forecasted service temperatures, coupled with modelling activities able to predict the microstructural evolution under these new conditions. The lack of widespread microstructural data for most commercial nickel base alloys in these time–temperature regimes makes this type of investigation even more important. In this study, the microstructural evolution of IN740, a Ni–Cr–Co–Mo–Nb–Ti–Al superalloy, is characterised as a function of aging conditions. A method for phase identification is described that can be confidently used to gather relevant information for modelling activity, such as: phase identity, volume fraction, size distribution and interparticle spacing. The microstructural evolution of IN740 is investigated at temperatures of 700 and 750°C for aging times up to 10 000 h. The data obtained experimentally from the aged specimens as well as from literature are used both as input for and validation of a microstructurally based continuum damage mechanics (CDM) model for forecasting creep properties. Using this predictive model, discussion is made of possible approaches needed to optimize creep performance.

Effect of thermal denaturation on the mechanical glass transition temperature of globular protein/co-solute systems

The work prepared high-solid mixtures of whey protein or bovine serum albumin with an amorphous co-solute (glucose syrup) and examined their glass transition behaviour at subzero temperatures. The interest in these condensed matrices was in relation to what extent thermal denaturation and subsequent aggregation of the proteinaceous molecules affects vitrification and, therefore, they were subjected to distinct heating regimes followed by cooling. Small-deformation dynamic oscillation in shear is known to respond to changes in network formation as a function of thermal treatment, albeit published reports thus far focused on low-solid aqueous hydrocolloid samples, and it has been chosen presently to examine the viscoelasticity of their high-solid counterparts. Results were further compared with those from a micromolecular technique, i.e. modulated differential scanning calorimetry. It appears that thermally induced cross-linking is readily recorded in what is known in the literature as the mechanical or network glass transition temperature, whereas the calorimetric Tg is not affected by the extent of polymeric associations in these mixtures. Further, the thermal protocol employed presently results in considerable differences in predictions of the mechanical Tg, which should reflect distinct three dimensional morphologies in these systems of globular protein and co-solute.

Cation and Anion Transport in a Dicationic Imidazolium-Based Plastic Crystal Ion Conductor

Here we investigate the organic ionic plastic crystal 1,2-bis[N-(N'-hexylimidazolium-d2(4,5))]ethane 2PF6(-) in one of its solid plastic crystal phases by means of multinuclear solid-state (SS) NMR and pulsed-field-gradient NMR diffusometry. We quantify distinct cation and anion diffusion coefficients as well as the Arrhenius diffusion activation energies (Ea) in this dicationic imidazolium-based plastic crystal. Our studies suggest a change in transport mechanism for the cation upon varying thermal and magnetic treatment (9.4 T), evidenced by differences in cation and anion Ea. Moreover, variable temperature (2)H SSNMR line shapes support a change in local molecular environment upon slow cooling in B0. We quantify the percentage of mobile anions as a function of temperature with (19)F SSNMR, wherein two distinct spectral features are present. We also comment on the Arrhenius pre-exponential factor for diffusion (D0), giving insight into the number of degrees of freedom for transport for both cation and anion as a function of thermal treatment. Given the breadth and depth of our measurements, we propose that bulk ion transport is dominated by anion diffusion in ionic-liquid-like domain boundaries separating crystallites. This study elucidates fundamental properties of this plastic crystal, and allows for a more general and deeper understanding of ion transport within such materials.

In situ infrared spectroscopic study of the reaction pathway of the direct synthesis of n-butanol from ethanol over MgAl mixed-oxide catalysts

The interaction of ethanol and its evolution to n-butanol over different MgAl mixed oxides derived from hydrotalcite precursors is studied by FTIR and in situ DRIFT-MS experiments. The evolution of different surface species is monitored as a function of thermal treatments. Acetaldehyde appears as a primary intermediate which converts over the mixed oxides to C4 products through the aldol condensation reaction. However, acetaldehyde also produces surface carboxylate species which compete for the active sites and make the condensation process less efficient.

Metal induced crystallization of amorphous silicon thin films studied by x-ray absorption fine structure spectroscopy

The role of thin metallic layer (Chromium or Nickel) in the crystallization of a-Si film has been studied using X-ray absorption fine structure spectroscopy (XAFS). The films were grown at different substrate temperatures in two different geometrical structures : (a) a 200 nm metal layer (Cr or Ni) was deposited on fused silica (FS) followed by 400 nm of a-Si and (b) the 400 nm a-Si layer was deposited on FS followed by 200 nm of metal layer. XAFS measurements at Cr K-edge and Ni K-edge were done at BM08 – GILDA beamline of the European Synchrotron Research Facility (ESRF, Grenoble, F) in fluorescence mode. To understand the evolution of the local structure of Cr/Ni diffusing from bottom to top and from top to bottom, total reflection and higher incidence angles were employed. The relative content of metal, metal oxide and metal silicides compounds on the upper surface and/or in the bulk of different films has been evaluated as a function of thermal treatment.

TiO2–Cu photocatalysts: a study on the long- and short-range chemical environment of the dopant

In this study, the short- and long-range chemical environments of Cu dopant in TiO2 photocatalyst have been investigated. The Cu-doped and undoped TiO2 specimens were prepared by the sol–gel approach employing CuSO4·5H2O and Ti(O-iPr)4 precursors and subjecting the dried gels to thermal treatment at 400 and 500 °C. The photocatalytic activity, investigated by methylene blue degradation under sunlight irradiation, showed a significantly higher efficiency of Cu-doped samples than that of pure TiO2. The X-ray diffraction results showed the presence of anatase phase for samples prepared at 400 and 500 °C. No crystalline CuSO4 phase was detected below 500 °C. It was also found that doping decreases the crystallite size in the (004) and (101) directions. Infrared spectroscopy results indicated that the chemical environment of sulfate changes as a function of thermal treatment, and UV–vis spectra showed that the band gap decreases with thermal treatment and Cu doping, showing the lowest value for the 400 °C sample. X-ray absorption fine structure measurements and analysis refinements revealed that even after thermal treatment and photocatalytic assays, the Cu2+ local order is similar to that of CuSO4, containing, however, oxygen vacancies. X-ray photoelectron spectroscopy data, limited to the near surface region of the catalyst, evidenced, besides CuSO4, the presence of Cu1+ and CuO phases, indicating the active role of Cu in the TiO2 lattice.