Scientific Papers in SCI

Abstract

A multi-element, time-dependent model is used to examine additive-assisted copper electroplating in macro-channels. This model is an adaptation of the work of Akolkar and Landau [J. Electrochem. Soc., 156, D351 (2009)], used to describe plating in micro-vias for integrated circuits. Using their method for describing species movement in the channel, the model has been expanded to include transport and adsorption limitations of the inhibitor and accelerator, as well as the copper ions in solution. The model is used to investigate copper plating as an infiltration method across many size scales and aspect ratios. Biomorphic graphite scaffolds produced from wood are used as a representative system and the results of a two-additive bath are used to characterize the behavior of the additives and determine the effectiveness of the plating. The results indicate that at macro-scales, channel dimensions play an increasingly important role in dictating the behavior of additive-assisted plating. Because additive systems are designed to establish differential surface coverage within the channel, the success of which is determined by the additive's rates of diffusion and adsorption, certain size scale/aspect ratio combinations preclude such coverage. A guide for sample geometries that may be successfully infiltrated with a two-additive bath is provided.

Abstract

In this paper, the sorption of arsenic onto nanocrystalline magnetite mineral Fe3O4 was studied in a model system. Nanocrystalline magnetite was produced by mechanical activation in a planetary ball mill from natural microcrystalline magnetite. As a consequence of milling, the specific surface area increased from 0.1 m2/g to 11.9 m2/g and the surface site concentration enhanced from 2.2 sites/nm2 to 8.4 sites/nm2. These changes in surface properties of magnetite lead to the enhancement of arsenic removal from model system. The best sorption ability was achieved with magnetite sample activated for 90 min. In this case the sample was able to absorb around 4 mg/g. The structural changes of magnetite were also observed and the new hematite phase was detected after 120 min of milling. A good correlation between the decreasing particle size, increasing specific surface area and reduction of saturation magnetization was found. In desorption study, KOH and NaOH were found as the best eluents where more than 70% of arsenic was released back into the solution. The principal novelty of the paper is that mineral magnetite, truly one nature's gift can be used after “smart” milling (mechanical activation) as an effective arsenic sorbent.

Abstract

ZrB2–Al2O3 nanocomposite powder was produced by aluminothermic reduction in Al/ZrO2/B2O3 system. In this research, high energy ball milling was used to produce the necessary conditions to induce a mechanically induced self-sustaining reaction. The ignition time of the composite formation was found to be about 13 min. The synthesis mechanism in this system was investigated by examining the corresponding sub-reactions as well as changing the stoichiometry of reactants. Thermal behavior of the system was also studied.

Abstract

A computational fluid dynamics (CFD) simulation study of the preferential oxidation of CO (CO-PROX) in microstructured reactors consisting in square and semicircular microchannels coated with an Au/CuOx–CeO2 catalyst is presented. The CO content of the feed stream was set at 1 vol.%. A parametric sensitivity analysis has been performed under isothermal conditions revealing that an optimal reaction temperature exists that leads to a minimum CO content at the microreactor exit. The influence of the space velocity, CO2 concentration and oxygen-to-CO molar ratio in the feed stream (λ), catalyst loading, and microchannel characteristic dimension (d) on the microreactor performance has been investigated. Under suitable conditions, the CO concentration can be reduced below 10 ppm at relatively low temperatures within the 155–175 °C range. A negative effect of the increase of d from 0.35 mm to 2.8 mm on the CO removal efficiency has been found and attributed to a more detrimental effect of the mass transport limitations on the oxidation of CO than that of H2. Non-isothermal CFD simulations have been performed to investigate the cooling of the CO-PROX reactor with air or a fuel cell anode off gas surrogate in parallel microchannels. Due to the very rapid heat transfer allowed by the microreactor and the strong influence of the reaction temperature on the exit CO concentration, a careful control of the coolant flow rate and inlet temperature is required for proper reactor operation. The microreactor behavior is virtually isothermal.

Abstract

Development of porous alumina has been the objective of numerous studies in recent decades, due to the intrinsic properties of aluminium oxide, such as high melting point, low thermal conductivity, chemical inertness and corrosion resistance which, in addition to a high surface area and permeability, make aluminas being used for many different industrial and technical applications. The crystallographic and textural stability of alumina acquires significant importance in those processes involving high temperatures; however, most of the synthesis methods yield metastable oxides of little interest in high-temperature processes due to the transformation to alpha phase, with the consequent reduction in surface area. The present article reviews diverse procedures for obtaining porous alumina with high specific surface area, including methods and strategies for preparing high surface alpha-alumina. Within this framework, the paper analyzes the results obtained through bioreplica of lignocellulosic materials. This technology allows preparing aluminas with the complex structural hierarchy of the lignocellulosic templates.

Abstract

TiO2 Degussa P25, TiO2 prepared by sol–gel submitted to sulfation pre-treatment and some metallized catalysts obtained by photodeposition of Au or Pt over the sulfated TiO2, were evaluated in the reaction of ethanol photo-oxidation. FT-IR spectroscopy was used to investigate the surface features of the photocatalysts, identifying adsorbed species and following the evolution of intermediate products in the ethanol photo-oxidation reaction. Nature of surface acidity in terms of Brönsted and Lewis centers was also studied.

Results showed that sulfation pre-treatment and metallization were important factors influencing the selectivity. Acetaldehyde was the main oxidation product on sulfated TiO2; in the case of P25 also acetates production was observed. The photodeposition of metals had a detrimental effect on the selectivity to acetaldehyde; on metallized catalysts the formation of stable secondary intermediates was detected.

Based on these findings, a reaction pathway for the ethanol photo-oxidation over the different photocatalysts, via acetaldehyde or via acetate formation is proposed.

Abstract

Pure A-La2Si2O7 powder has been synthesized through a spray pyrolysis method followed by calcination at 1100 degrees C for 15 h. The crystallographic structure, refined from the synchrotron powder diffraction pattern of the sample, showed tetragonal symmetry with space group P4(1), a = 6.83565(1) angstrom, and c = 24.84133(1) angstrom. The Si-29 and La-139 NMR spectra have been described here for the first time in the literature and could be simulated with four Si and four La resonances, respectively, in good agreement with the presence of four Si and four La crystallographic sites in the unit cell. The same synthesis method was 2 successful for the synthesis of Eu3+-doped A-La2Si2O7 (%Eu = 3-40). The analysis of the unit cell volumes indicated that Eu3+ replaces La3+ in the unit cell for all Eu3+ substitution levels investigated. However, anomalous diffraction data indicated that the La/Eu substitution mechanism was not homogeneous, but Eu much prefers to occupy the RE3 sites. The Eu-doped A-La2Si2O7 phosphors thus synthesized exhibited a strong orange-red luminescence after excitation at 393 nm. Lifetime measurements indicated that the optimum phosphor was that with an Eu3+ content of 20%, which showed a lifetime of 2.3 ms. The quantum yield of the latter was found to be 12% at 393 nm excitation. These experimental observations together with the high purity of the phase obtained by the proposed spray pyrolysis method make this material an excellent phosphor for optoelectronic applications.

Abstract

WSex films with variable Se/W ratio were deposited by non-reactive r.f. magnetron sputtering from WSe2 target changing the applied d.c. pulsed bias conditions and substrate temperature. The structural and chemical properties were measured by cross-sectional scanning electron microscopy (X-SEM), energy dispersive analysis (EDX), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The tribological properties were measured in ambient air (RH = 30–40%) and dry nitrogen by means of a reciprocating ball-on-disk tribometer. A clear correlation was found between the Se/W ratio and the measured friction coefficient displaying values below 0.1 (in ambient air) and 0.03 (in dry N2) for ratios Se/W ≥ 0.6 as determined by electron probe microanalysis (EPMA). The results demonstrated that notable tribological results could be obtained even in ambient air (friction ≤ 0.07 and wear rate ≈10−7 mm3 Nm−1) by controlling the film microstructure and chemical composition. By incorporating carbon, wear and chemical resistance can be gained by formation of non-stoichiometric carbides and/or alloying into the defective WSex hexagonal structure. The existence of a WSe2 rich interfacial layer (either on the ball scar or embedded in the film track) was evidenced by Raman in low friction conditions. The improvement in tribological performance is therefore obtained by means of layered WSex, the formation of gradient composition from metallic W (hard) to WSe2 (lubricant) and carbon incorporation.

Abstract

The aim of this study is to elucidate the coarsening kinetics involved during densification of fine-grained pure α-alumina by spark plasma sintering. Low temperature and short dwell time sintering conditions were used to preserve the nanocrystalline structure of the starting commercial powder (about 50 nm). Notwithstanding the above, submicron grain coarsened microstructures have been developed. The microstructure evolution of alumina under different sintering conditions points to a nanograin rotation densification mechanism as being responsible for the fast grain growth observed.

Abstract

The thermal conductivity of wood-derived graphite and graphite/copper composites was studied both experimentally and using finite element analysis. The unique, naturally-derived, anisotropic porosity inherent to wood-derived carbon makes standard porosity-based approximations for thermal conductivity poor estimators. For this reason, a finite element technique which uses sample microstructure as model input was utilized to determine the conductivity of the carbon phase independent of porosity. Similar modeling techniques were also applied to carbon/copper composite microstructures and predicted conductivities compared well to those determined via experiment.

Abstract

Aqueous hydrolysis of a series of cerium-containing polyoxotitanium cages gives Ce(III)-doped TiO2 [TiO2(Ce)] or TiO2-supported Ce(III)2Ti2O7, depending on the starting Ti : Ce ratio of the precursor. TiO2-supported Ce2Ti2O7 exhibits superior photocatalytic activity to the Ce-doped TiO2 materials and unusual broad-band absorption behaviour across the visible and near-infrared regions.

Abstract

Pairs of samples containing Ag nanoparticles (NPs) of different dimensions have been produced under the same conditions but on different substrates, namely standard glass slides and a thin layer of amorphous aluminum oxide (a-Al2O3) on-glass. Upon storage in ambient conditions (air and room temperature) the color of samples changed and a blue-shift and damping of the surface plasmon resonance was observed. The changes are weaker for the samples on-glass and tend to saturate after 12 months. In contrast, the changes for the samples on a-Al2O3 appear to be still progressing after 25 months. While x-ray photoelectron spectroscopy shows a slight sulfurization and negligible oxidation of the Ag for the on-glass samples upon 25 months aging, it shows that Ag is strongly oxidized for the on a-Al2O3 samples and sulfurization is negligible. Both optical and chemical results are consistent with the production of a shell at the expense of a reduction of the metal core dimensions, the latter being responsible for the blue-shift and related to the small (<10 nm initial diameter) of the NPs. The enhanced reactivity of the Ag NPs on the a-Al2O3 supports goes along with specific morphological changes of the Ag NPs and the observation of nitrogen.

Abstract

A set of three catalysts (a Au–Ni bimetallic and their corresponding Au and Ni monometallics) has been prepared by impregnation of previously prepared suspensions of monodisperse metallic particles to ensure the precise control of their physicochemical characteristics (size and composition). The Au–Ni/CeO2 bimetallic catalysts present better reactivity toward CO oxidation than monometallic Au/CeO2 and Ni/CeO2 prepared under identical conditions. “operando-like” characterization of Ni and Au atoms into the bimetallic particles using, among other techniques, ambient-pressure photoelectron spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy has allowed us to determine that under oxidative conditions the samples present a Au@NiO core–shell distribution, where Ni surface atoms are affected by an electronic effect from inner Au atoms.

Abstract

Se presenta un procedimiento para la planificación de recogida y flujo de los residuos sólidos (de construcción y demolición, hormigón, cerámica, vidrio y otros) basado en la utilización de una herramienta informatizada, para conseguir una optimización de su gestión. Dicho procedimiento parte de normativa establecida según un Plan Director Territorial de la Gestión de Residuos Sólidos Urbanos (RSU) aprobado en una Comunidad Autónoma, en este caso se particulariza a la de Andalucía, tomando como ejemplo el volumen de residuos que se producen en una colectividad de tamaño medio (provincia de Almería), siendo extensible a otras mayores en población y territorio, disponiendo de datos actualizados.
El procedimiento utiliza una herramienta informática de gran difusión en el mundo, como es Google Earth y, de este modo, genera un número de “Centros deTransferencia” con objeto de minimizar el gasto de transporte, partiendo de una premisa previa en cuanto a distancia entre núcleos poblacionales y centros de tratamiento. Los Centros generados con la aplicación del procedimiento se pueden visualizar en un mapa topográfico, con áreas de influencia y vías de acceso a los mismos y se le pueden asociar una serie de datos tabulados con información adicional de utilidad. El procedimiento propuesto se va retroalimentando de manera constante con datos reales e información de campo, permitiendo a las empresas que producen residuos de distinta tipología como son los residuos de construcción y demolición principalmente, pero también hormigón, cerámica, vidrio, mezclas de todos ellos, residuos clasificados como peligrosos e incluso de otros materiales, a la propia administración y a la sociedad, en general, conocer las tasas de cada planta de tratamiento y qué se hace con los residuos entregados para contribuir a la reducción del impacto medioambiental de los mismos y a su gestión sostenible.
 

Abstract

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

Abstract

BiVO₄ hierarchical structures were synthesized by means of a surfactant free hydrothermal method having good photoactivities for the degradation of Methylene Blue and Rhodamine B under UV–vis irradiation. From the structural and morphological characterization it has been stated that BiVO₄ present the monoclinic crystalline phase with different morphologies depending on the pH value. For Methylene Blue the photodegradation rate is strongly affected by the crystallite size and higher (0 0 4) facet exposition. On the contrary, for Rhodamine B, the ζ-potential of the surface clearly determines the photocatalytic performance of BiVO₄ catalyst.

Abstract

A comparative study of both conventional rising temperature and sample-controlled methods, like constant rate thermal analysis (CRTA), is carried out after analyzing a set of solid state reactions using both methods. It is shown that CRTA avoids the influence of heat and mass transfer phenomena for a wide range of sample sizes leading to reliable kinetic parameters. On the other hand, conventional rising temperature methods yield α–T plots dependent on experimental conditions, even when using samples sizes smaller than 2 mg. Moreover, it is shown that the discrimination of overlapping processes is dramatically improved using sample-controlled methods instead of conventional heating procedures. An advanced method for performing the kinetic analysis of complex processes from a single CRTA experiment is proposed.

Abstract

The thermal degradation kinetics of several ethylene–propylene copolymers (EPM) and ethylene–propylene–diene terpolymers (EPDM), with different chemical compositions, have been studied by means of the combined kinetic analysis. Until now, attempts to establish the kinetic model for the process have been unsuccessful and previous reports suggest that a model other than a conventional nth order might be responsible. Here, a random scission kinetic model, based on the breakage and evaporation of cleavaged fragments, is found to describe the degradation of all compositions studied. The suitability of the kinetic parameters resulting from the analysis has been asserted by successfully reconstructing the experimental curves. Additionally, it has been shown that the activation energy for the pyrolysis of the EPM copolymers decreases by increasing the propylene content. An explanation for this behavior is given. A low dependence of the EPDM chemical composition on the activation energy for the pyrolysis has been reported, although the thermal stability is influenced by the composition of the diene used.

Abstract

A series of synthesised TiO2-based and commercial photocatalysts were modified by Pt photodeposition and a study made of their photocatalytic activity in hydrogen production. The modified commercial photocatalysts were Evonik P25, Kronos vlp7000 and Hombikat UV-100, and the other modified photocatalysts were synthesised by our group using sol–gel and sol–gel hydrothermal processes (SG400, SG750 and HT). Pt weight percentages used in the study were 0.5, 1.0 and 2.1 wt.% (Pt/TiO2). The photocatalysts were extensively characterised by X-ray diffraction (XRD), UV–vis diffuse reflectance, Brunauer–Emmett–Teller (BET) surface area measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM–EDX), Fourier transform infrared spectroscopy (FTIR) and laser light dispersion. Methanol (25% vol.) was used as sacrificial agent over the 8 h of the hydrogen production tests and measurements were taken of the final concentrations of formaldehyde and formic acid as well as initial and final TOC. Photoactivity of all photocatalysts increased in the presence of Pt. The most efficient of the synthesised photocatalysts was SG750 and of the commercial photocatalysts P25. Maximum production of SG750 was 1846 μmol h−1 at 1.0 wt.% Pt and its production per surface unit was notably higher than that of P25.

Abstract

Erbium doped TiO2–Bi2WO6 have been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Rhodamine B. From the structural and morphological characterization it has been stated that the presence of Er3+ induces a progressive russelite cell contraction due to its incorporation in the Bi2WO6 lattice in substitutional sites. The best photocatalytic performance was attained for the samples with 1 at% of Er. From the study of the photocatalytic activity under different irradiation conditions it can be inferred that Er3+ presence induces a significant improvement of the photoactivity in the UV range. The evolution of band-gap values seems to be similarly related with the reaction rate progression. Thus, the higher band-gap values in lower Er doped systems would be the cause of a better electron hole separation under UV irradiation.

Abstract

A computerized database was created, based on a Geographic Information System (GIS), with hyperlinks to the website for a Rural Development Association (Almería province, Andalusia, Spain). Thus, a catalogue of traditional rural buildings in this particular area was compiled, identifying and characterizing each one, establishing criteria for a dynamic and rational selection. The purpose to select this example was to facilitate their management by public organizations or private individuals, for their reuse, restoration or both. The cataloguing and promotion of rural architecture will contribute to creating jobs by stimulating new economic activity, such as the promotion of cultural tourism, while preserving a valuable source of information on rural culture, recovering local construction techniques, encouraging a sense of community, and making villages and rural areas more attractive to visitors. The assessment of the rehabilitation potential of rural buildings in this region has helped to establish a priority order for their reuse, and so an intervention map has been devised in terms of a “Decision Index” corresponding to each considered building.

Abstract

Which mechanisms mediate cell attachment to biomaterials? What role does the surface charge or wettability play on cell–material anchorage? What are the currently investigated strategies to modify cell–matrix adherence spatiotemporally? Considering the development of scaffolds made of biocompatible materials to temporarily replace the structure and/or function of the extracellular matrix, focus is given to the analysis of the specific (i.e., cell adhesive peptide sequences) and unspecific (i.e., surface charge, wettability) mechanisms mediating cell-matrix interactions. Furthermore, because natural tissue regeneration is characterized by the dynamic attachment/detachment of different cell populations, the design of advanced scaffolds for tissue engineering, based in the spatiotemporal tuning of cell–matrix anchorage is discussed.

Abstract

Nanometric powdered TixTa1−xC0.5N0.5-based cermets were fabricated using a mechanically induced self-sustaining reaction and consolidated by spark plasma sintering. Highly dense cermets were obtained, and their chemistry, microstructure and mechanical properties were characterised by X-ray diffraction, scanning electron microscopy, image analysis, microindentation and nanoindentation. The microhardness was found to depend directly on the contiguity and size of the ceramic hard particles. The samples synthesised at the lowest temperature (1150 °C) exhibited more homogeneous microstructures and smaller ceramic particles and the best combination of microhardness and fracture toughness.

Abstract

Porous Bragg microcavities formed by stacking a series of porous nanocolumnar layers with alternate low (SiO2) and high (TiO2) refractive index materials have been prepared by physical vapor deposition at glancing angles (GLAD). By strictly controlling the porosity and refractive index of the individual films, as well as the relative orientation of the nanocolumns from one layer to the next, very porous and nondispersive high optical quality microcavities have been manufactured. These photonic structures have been implemented into responsive devices to characterize liquids, mixtures of liquids, or solutions flowing through them. The large displacements observed in the optical spectral features (Bragg reflector gap and resonant peak) of the photonic structures have been quantitatively correlated by optical modeling with the refractive index of the circulating liquids. Experiments carried out with different glucose and NaCl solutions and mixtures of water plus glycerol illustrate the potentialities of these materials to serve as optofluidic devices to determine the concentration of solutions or the proportion of two phases in a liquid mixture.

Abstract

Highly oriented CrO₂ thin films have been heteroepitaxially grown on TiO₂ rutile (110), (100) and (001) single crystalline substrates, by Low Pressure Chemical Vapor Deposition from CrO₃ as precursor and flowing oxygen as carrier gas, under a pressure of 67 Pa. The experimental conditions were fine tuned by depositing on polycrystalline Ti foils, to improve the purity of the films and the deposition rate. A maximum deposition rate of 175 nm h^− 1 was obtained.

The composition and texture of films, up to 2 μm thick, have been determined by X-ray diffraction (XRD) and Micro Raman, while their microstructure has been examined by Scanning Electron Microcopy and Atomic Force Microscopy, and their magnetic behavior has been tested by superconducting quantum interference device magnetometry. These techniques reveal that the phase purity, texture, microstructure and thickness of these films are dependent on the crystalline face of the rutile substrate and the deposition temperature. Thus, microscopy techniques, XRD and Raman spectroscopy confirm that highly textured CrO₂ films were always obtained on the three rutile substrate faces when deposition temperature ranges between 616 K and 636 K. But these techniques also show that CrO₂ films are unpurified with inclusions or patches of Cr₂O₃, for the most of the substrates and especially at high deposition temperatures. Magnetic measurements conclusively demonstrate that pure CrO₂ films are only obtained when TiO₂ (110) is used as a substrate.

Abstract

The use of RE2Si2O7 materials as environmental barrier coatings (EBCs) and in the sintering process of advanced ceramics demands a precise knowledge of the coefficient of thermal expansion of the RE2Si2O7. High-temperature X-ray diffraction (HTXRD) patterns were collected on different RE2Si2O7 polymorphs, namely A, G, α, β, γ, and δ, to determine the changes in unit cell dimensions. RE2Si2O7 compounds belonging to the same polymorph showed, qualitatively, very similar unit cell parameters behavior with temperature, whereas the different polymorphs of a given RE2Si2O7 compound exhibited markedly different thermal expansion evolution. The isotropy of thermal expansion was demonstrated for the A-RE2Si2O7 polymorph while the rest of polymorphs exhibited an anisotropic unit cell expansion with the biggest expansion directed along the REOx polyhedral chains. The apparent bulk thermal expansion coeficcients (ABCTE) were calculated from the unit cell volume expansion for each RE2Si2O7 compound. All compounds belonging to the same polymorph exhibited similar ABCTE values. However, the ABCTE values differ significantly from one polymorph to the other. The highest ABCTE values correspond to A-RE2Si2O7 compounds, with an average of 12.1 × 10−6 K−1, whereas the lowest values are those of β- and γ-RE2Si2O7, which showed average ABCTE values of ~4.0 × 10−6 K−1.

Abstract

We study in this paper the conversion of CaO-based CO2 sorbents when subjected to repeated carbonation–calcination cycles with a focus on thermally pretreated/doped sorbents. Analytical equations are derived to describe the evolution of conversion with the cycle number from a unifying model based on the balance between surface area loss due to sintering in the looping-calcination stage and surface area regeneration as a consequence of solid-state diffusion during the looping-carbonation stage. Multicyclic CaO conversion is governed by the evolution of surface area loss/regeneration that strongly depends on the initial state of the pore skeleton. In the case of thermally pretreated sorbents, the initial pore skeleton is highly sintered and regeneration is relevant, whereas for nonpretreated sorbents the initial pore skeleton is soft and regeneration is negligible. Experimental results are obtained for sorbents subjected to a preheating controlled rate thermal analysis (CRTA) program. By applying this preheating program in a CO2 enriched atmosphere, CaO can be subjected to a rapid carbonation followed by a slow rate controlled decarbonation, which yields a highly sintered skeleton displaying a small conversion in the first cycle and self-reactivation in the next ones. Conversely, carbonation of the sorbent at a slow controlled rate enhances CO2 solid-state diffusion, which gives rise, after a quick decarbonation, to a highly porous skeleton. In this case, CaO conversion in the first cycle is very large but it decays abruptly in subsequent cycles. Data for CaO conversion retrieved from the literature and from further experimental measurements performed in our work are analyzed as influenced by a variety of experimental variables such as preheating temperature program, preheating exposition time, atmosphere composition, presence of additives, and carbonation–calcination conditions. Conversion data are well fitted by the proposed model equations, which are of help for a quantitative interpretation of the effect of experimental conditions on the multicyclic sorbent performance as a function of sintering/regeneration parameters inferred from the fittings and allow foreseeing the critical conditions to promote reactivation. The peculiar behavior of some pretreated sorbents, showing a maximum conversion in a small number of cycles, is explained in light of the model.

Abstract

Gas-solid heterogeneous photocatalytic oxidation (PCO) of cyclohexane in humidified air over TiO2 and Pt/TiO2 catalyst was studied.

Pt/TiO2 photocatalysts were synthesized by photodeposition method at different Pt loadings (0.5–2 wt.%). The addition of 0.5 wt.% Pt does not significantly modify the TiO2 properties. The increase in Pt loading induces to an aggregation of metallic particles on TiO2 surface.

The cyclohexane PCO was performed in a fluidized bed photoreactor at 60 and 100 °C. Pure TiO2 was more active than 1 and 2 wt.% Pt/TiO2 samples at 60 °C. Nevertheless, the conversion level increases with temperature on Pt/TiO2 photocatalysts. The cyclohexane was mineralized into CO2, water and low amount of CO. A beneficial effect of Pt addition was found, since total CO2 selectivity was obtained. The Pt/TiO2 photocatalysts prepared by photodeposition provide the total cyclohexane PCO without CO production. Photocatalysts deactivation was not observed in any performed test. Evidence of an opportune tuning of temperature is highlighted.

Abstract

A new type of nanostructured selective ultraviolet (UV) reflecting mirror is presented. Periodic porous multilayers with photonic crystal properties are built by spin-coating-assisted layer-by-layer deposition of colloidal suspensions of nanoparticles of ZrO2 and SiO2 (electronic band gap at λ < 220 nm). These optical filters are designed to block well-defined wavelength ranges of the UVA, UVB, and UVC regions of the electromagnetic spectrum while preserving transparency in the visible. The shielding against those spectral regions arises exclusively from optical interference phenomena and depends only on the number of stacked layers and the refractive index contrast between them. In addition, it is shown that the accessible pore network of the as-deposited multilayer allows preparing thin, flexible, self-standing, transferable, and adaptable selective UV filters by polymer infiltration, without significantly losing reflectance intensity, i.e., preserving the dielectric contrast. These films offer a degree of protection comparable to that of traditional ones, without any foreseeable unwanted secondary effects, such as photodegradation, increase of local temperature or, as is the case for organic absorbers, generation of free radicals, all of which are caused by light absorption.