Scientific Papers in SCI

Abstract

Usually, nanoparticle synthesis methodologies require the use of organic molecules (capping agent, solvent molecules, etc.), which results in carbon deposits on the nanoparticle surface. These residues modify the surface properties mainly affecting the catalytic behavior. In this work, unsupported poly(vinylpyrrolidone) (PVP)-stabilized PtCu (1:3 molar ratio) bimetallic alloy nanoparticles were synthetized and characterized. An alternative surface cleaning method has been designed, which successfully removes the presence of organic fragments. To address this key issue, we have combined a first nanoparticle washing step with a near ambient pressure X-ray photoelectron spectroscopy (NAPXPS) study in order to obtain a clean active site and the total understanding of the carbon elimination mechanism. The dynamic evolution of the surface organic species composition under different gas mixtures at 750 mTorr and 350 degrees C has been studied, and only under CO2 exposure, NAPXPS analysis revealed a total availability of the active site by the removal of the organic nanoparticle coating.

Abstract

Mg2SiO4-MgAl2O4 eutectic ceramics have been fabricated by means of the laser floating zone (LFZ) technique. The microstructure has revealed as an unusual one at lower growth rate, composed of broken lamellae of MgAl2O4 distributed randomly along one matrix, composed of Mg2SiO4. At higher growth rates, a cell structure with intra-cell lamella structure is dominant. Contrary to most eutectic systems, hardness is not dependent upon the inter-spacing, but it does depend on one characteristic length of lamellae: their perimeter. One simple model based upon the dislocation is proposed, which successfully accounts for such extraordinary hardness law. Accordingly, Mg2SiO4-MgAl2O4 eutectic ceramics fabricated at 50 mm/h growth rate with the smallest MgAl2O4 lamella perimeter favorably showed more elevated hardness (13.4 GPa from Vickers indentation and 15.3 GPa from nanoindentation) and strength (430 MPa) than those found in the monolithic Mg2SiO4 matrix.

Abstract

Fischer Tropsch's reaction, known from 1925, receives special attention nowadays due to its key role in the CO2 or biomass valorization to liquid fuels and chemicals. Several aspects on the exact mechanism or the role of water in this reaction are not yet completely clear. Formyl species, HCO, have been proposed as the most probable reaction intermediate, but they have never been observed under operation conditions closed to the real ones. In this work, using DRIFTS-MS operando techniques, HCO intermediates are detected under a H2/CO flow and 200 °C. IR bands at 2900 cm−1 and 1440 cm−1 attributed to ν(C–H) and δ(HCO) vibrations modes characterize these species. Evolution of these bands with the reaction time evidences its high reactivity with OH groups, which explains the positive effect of water on the CO conversion previously observed.

Abstract

We carried out a rational design of catalyst supports by high-energy ball milling. Tailored mixtures of TiO2 crystalline phases were obtained using rotational speed and milling time as variable parameters. Polymorphic transformation from anatase to rutile through high-pressure TiO2 (II) as intermediate was confirmed by X-ray Diffraction (XRD), Raman Spectroscopy and Transmission Electron Microscopy (TEM). Also, starting material doubled its specific surface area due to particle fragmentation, as confirmed by surface area of Brunauer-Emmet-Teller (S-BET) and Scanning Electron Microscopy (SEM). Defects introduced during milling process generated oxygen vacancies in the surface and bulk of supports, as evidenced by X-ray Photoelectron Spectroscopy (XPS) and Electron Paramagnetic Resonance (EPR). Furthermore, longer milling time increased reducibility and oxygen mobility of supports, as observed by H-2 Temperature Programmed Reduction (H-2-TPR) and O-2 Temperature Programmed Desorption (O-2-TPD). Phase composition remained unchanged even under extreme conditions, highlighting the stability of unusual TiO2 (II) phase. Properties achieved in present materials could benefit metal-support interactions and play a major role in supported catalysts. 

Abstract

A model for high-temperature plasticity of polycrystals controlled by disclination dipoles is proposed that predict a parabolic dependence of the strain rate versus the applied stress. The presence of a precise stationary disclination density explains the origin of plasticity without microstructural invariance, commonly known as superplasticity. The disclination mechanism is universal, although other processes, such as dislocation glide, are superposed to this one in many systems such as metals or metallic alloys. While, in ceramics it is likely to be the only operative mechanism. Activation of disclination dipoles is a necessary condition for plasticity and sufficient one for superplastic yielding. 

Abstract

A conventional Pt/CeO2/Al(2)O(3)catalyst physically mixed with an ionic conductor (Mo- or Eu-doped ZrO2) was tested at high space velocity (20,000 h(-1)and 80 L h(-1)g(cat)(-1)) under model conditions (only with CO and H2O) and industrial conditions, with a realistic feed. The promoted system with the ionic conductor physically mixed showed better catalytic activity associated with better water dissociation and mobility, considered as a rate-determining step. The water activation was assessed by operando diffuse reflectance infrared fourier transformed spectroscopy (DRIFTS) studies under reaction conditions and the Mo-containing ionic conductor exhibited the presence of both dissociated (3724 cm(-1)) and physisorbed (5239 cm(-1)) water on the Eu-doped ZrO(2)solid solution, which supports the appearance of proton conductivity by Grotthuss mechanism. Moreover, the band at 3633 cm(-1)ascribed to hydrated Mo oxide, which increases with the temperature, explains the increase of catalytic activity when the physical mixture was used in a water gas shift (WGS) reaction.

Abstract

In the current study, synthesis and detailed characterization of cellulose biochars as a waste biomass model component and vine shoot biochars as a real waste biomass catalyst was performed. Although initially biochars exhibit poor textural properties, a simple activation process can make them much more suitable as a catalyst supports. A combination of physical (CO2) and chemical activation (ZnCl2) was evaluated. The characterization results indicated that the surface area and pore volume of the biochars have increased significantly by chemical activation treatment with ZnCl2. A series of metal catalysts (Pd, Au and Ru) supported on biochars was prepared and characterized. The prepared materials represent a set of noble metal catalysts supported on biochars with different textural and surface properties, which can be used to evaluate the catalytic role of the active phase and carbon support nature in catalytic reactions of interest, such as hydrodeoxygenation, described in the part II.

Abstract

Soot and particulate emissions from the transport sector are a major concern worldwide, given their harmful effects on public health and the environment. On-road vehicles are the main contributing source to this kind of pollution. They are strictly regulated in many countries, with limitations on the number and concentration of released particles, and they must be equipped with particle abatement systems. Wall-flow particulate filters are the most popular and effective devices to reduce particulate emissions from diesel and gasoline vehicles. Diesel Particulate Filters (DPFs) have been a recurrent research topic since the last century. There are different research studies analysing different aspects of these systems, at different levels, using different methodologies and different approaches. Their results are not always comparable. This work analyses the latest advances and trends in this technology by comparing two relevant performance parameters: their filtration efficiency and pressure drop. The findings of this study suggest that, in order to be competitive, upcoming DPFs should have filtration efficiencies above 80%, and pressure drops below 10 kPa, for space velocities of 1.5.10(5) h(-1) or more at the clean state. They should reach similar to 100% efficiency after a short operation period, before the soot load reaches 0.2 g/L. Later, they should keep a low pressure drop for a longer time, with a reference of no more than 13 kPa for 6 g/L of soot load. Based on this analysis, this work proposes some test criteria and suggestions for the main parameters. 

Abstract

The present recommendations have been developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The recommendations provide guidance on kinetic analysis of multi-step processes as measured by thermal analysis methods such as thermogravimetry (TGA) and differential scanning calorimetry (DSC). Ways of detecting the multi-step kinetics are discussed first. Then, four different approaches to evaluation of kinetic parameters (the activation energy, the pre-exponential factor, and the reaction model) for individual steps are considered. The approaches considered include multi-step model-fitting as well as distributed reactivity, isoconversional, and deconvolution analyses. For each approach practical advice is offered on its effective usage. Due attention is also paid to the typical problems encountered and to the ways of resolving them. The objective of these recommendations is to help a non-expert with efficiently performing multi-step kinetic analysis and interpreting its results.

Abstract

Free-standing and flexible biocomposite films formed by a polyaleuritate matrix and nanocellulose fillers (i.e., cellulose nanofibrils) have been fabricated by a sustainable process. For this, 9,10,16-trihydroxyhexadecanoic (aleuritic) acid from shellac and nanocellulose were blended at different ratios in water through a sonication process. Polymerization of the polyhydroxylated fatty acid into polyaleuritate was induced by a solvent-free, melting polycondensation reaction in the oven. These biocomposites were characterized to evaluate their chemical (by ATR-FTIR spectroscopy) and physical (e.g., density, thermal stability, rigidity, gas permeability, surface energy, etc.) properties. The compatibility between the polyester matrix and the polysaccharide fillers was excellent due to the interaction by H bonds of the polar groups of both components. The addition of nanocellulose increased all determined mechanical parameters as well as the wettability and the barrier properties, while the thermal stability and the water uptake were determined by the polyaleuritate matrix. The physical properties of these biocomposites were compared to those of petroleum-based plastics and bio-based polymers, indicating that the developed materials can represent a sustainable alternative for different applications such as packaging.

Abstract

The large area scalable fabrication of supported porous metal and metal oxide nanomaterials is acknowledged as one of the greatest challenges for their eventual implementation in on-device applications. In this work, we will present a comprehensive revision and the latest results regarding the pioneering use of commercially available metal phthalocyanines and porphyrins as solid precursors for the plasma-assisted deposition of porous metal and metal oxide films and three-dimensional nanostructures (hierarchical nanowires and nanotubes). The most advanced features of this method relay on its ample general character from the point of view of the porous material composition and microstructure, mild deposition and processing temperature and energy constrictions and, finally, its straightforward compatibility with the direct deposition of the porous nanomaterials on processable substrates and device-architectures. Thus, taking advantage of the variety in the composition of commercially available metal porphyrins and phthalocyanines, we present the development of metal and metal oxides layers including Pt, CuO, Fe2O3, TiO2, and ZnO with morphologies ranging from nanoparticles to nanocolumnar films. In addition, we combine this method with the fabrication by low-pressure vapor transport of single-crystalline organic nanowires for the formation of hierarchical hybrid organic@metal/metal-oxide and @metal/metal-oxide nanotubes. We carry out a thorough characterization of the films and nanowires using SEM, TEM, FIB 3D, and electron tomography. The latest two techniques are revealed as critical for the elucidation of the inner porosity of the layers.

Abstract

Semiconductor photocatalysis is regarded as most privileged solution for energy conversion and environmental application. Recently, photocatalysis methods using bismuth-based photocatalysts, such as BiPO4, have been extensively investigated owing to their superior efficacy regarding organic pollutant degradation and their further mineralization into CO2 and H2O. It is well known that BiPO4 monoclinic phase exhibited better photocatalytic performance compared to Degussa (Evonik) P25 TiO2 in term of ultraviolet light driven organic pollutants degradation. However, its wide band gap, poor adsorptive performance and large size make BiPO4 less active under visible light irradiation. However, extensive research works have been conducted in the past with the aim of improving visible light driven BiPO4 activity by constructing a series of heterostructures, mainly coupled with π-conjugated architecture (e.g., conductive polymer, dye sensitization and carbonaceous materials). However, a critical review of modified BiPO4 systems using π-conjugated materials has not been published to date. Therefore, this current review article was designed with the aim of presenting a brief current state-of-the-art towards synthesis methods of BiPO4 in the first section, with an especial focuses onto its crystal-microstructure, optical and photocatalytic properties. Moreover, the most relevant strategies that have been employed to improve its photocatalytic activities are then addressed as the main part of this review. Finally, the last section presents ongoing challenges and perspectives for modified BiPO4 systems using π–conjugated materials

Abstract

Mixed-halide perovskites represent a particularly relevant case within the family of lead-halide perovskites. Beyond their technological relevance for a variety of optoelectronic devices, photoinduced structural changes characteristic of this type of material lead to extreme photophysical changes that are currently the subject of intense debate. Herein we show that the conspicuous photoinduced phase segregation characteristic of these materials is primarily the result of the local and metastable rearrangement of the iodide sublattice. A local photophysical study comprising spectrally resolved laser scanning confocal microscopy is employed to find a correlation between the defect density and the dynamics of photoinduced changes, which extend far from the illuminated region. We observe that iodide-rich regions evolve much faster from highly defective regions. Also, by altering the material composition, we find evidence for the interplay between the iodide-related defect distribution and the intra- and interdomain migration dynamics giving rise to the complexity of this process.

Abstract

Char based metallic (Pd-Au-Ru-Pt/C) catalysts have drawn increasing research interest due to their versatility in biomass related industrial reactions. Recent studies dealing with the synthesis of char-based catalysts in one single step (one-pot) use reductant atmospheres for biomass pyrolysis. In this work, the influence of the use of a reductant N2/H2 atmosphere on the physicochemical properties of the resulting chars was evaluated in comparison with the use of an inert N2 atmosphere. Specifically, the fundamental parameter of the pyrolysis process, the temperature, was evaluated in the 500−900 °C range. Produced chars were fully characterized by N2 isotherms, ultimate CHNS analysis, X-ray Diffraction, Raman spectroscopy, Diffuse Reflectance Infrared spectroscopy, X-ray Photoelectron spectroscopy, helium Temperature Programmed Decomposition and Isoelectric Point analysis. Slow pyrolysis under reductant atmosphere favours deoxygenation reaction against dehydrogenation ones, reduces the carbon yield and results in chars with a more hydrophobic and graphitic character, higher thermal stability and weak surface functionalization. The use of intermediates temperatures (700 °C) favours the obtaining of chars with suitable physicochemical properties and good surface functionalization, which will facilitate the anchoring of the active phase on the surface, improving the metallic dispersion of the resulting one pot catalyst. This leads us to affirm that the use of reducing atmospheres at intermediate temperatures, is superior to the use of inert atmospheres for this purpose. This analysis on the impact of the use of a reductant atmosphere during slow pyrolysis of microcrystalline cellulose opens a new working path for the optimization of char-based catalysts obtained in a single stage.

Abstract

Catalytic hydrodeoxygenation (HDO) is a fundamental and promising route for bio-oil upgrading to produce petroleum-like hydrocarbon fuels or chemical building blocks. One of the main challenges of this technology is the demand of high-pressure H-2, which poses high costs and safety concerns. Accordingly, developing cost-effective routes for biomass or bio-oil upgrading without the supply of commercial H-2 is essential to implement the HDO at commercial scale. This article critically reviewed the very recent studies relating to the novel strategies for upgrading the biofeedstocks with 'green' H-2 generated from renewable sources. More precisely, catalytic transfer hydro-genation/hydrogenolysis, combined reforming and HDO, combined metal hydrolysis and HDO, water-assisted in-situ HDO and nonthermal plasma technology and self-supported hydrogenolysis are reviewed herein. Current challenges and research trends of each strategy are also proposed aiming to motivate further improvement of these novel routes to become competitive alternatives to conventional HDO technology.

Abstract

Optical properties of polycrystalline molybdenum are determined from ultraviolet up to extreme ultraviolet by reflection electron energy loss spectroscopy (REELS). Calculations are performed within the dielectric response theory by means of the quantitative analysis of electron energy losses at surfaces QUEELS-epsilon (k, omega)-REELS software [Surf. Interface Anal. 36, 824 (2004)] that allows the simulation of inelastic scattering cross sections, using a parametric energy loss function describing the optical response of the material. From this energy loss function, the real and imaginary parts of the dielectric function, the refractive index, and the extinction coefficient are deduced and compared with previously published results.

Abstract

Semi-transparent perovskite solar cells have the competitive edge of being employed for building integrated photovoltaics due to their esthetic benefits as light harvesting windows/facades. Perovskites have received considerable attention in recent years as a thin film photovoltaic alternative, that can also be tweaked for its transparency, evolving from potentially high bandgaps that are suited for semi-transparent solar cell fabrication. Due to the existing trade of between the efficiency and transparency of a perovskite solar cell, tuning the band gap can address this by making a bridge between the aforementioned parameters. We report our findings on the use of a wide-bandgap perovskite MAPbBr₃, with a rational energetic level hole transport materials based on polycyclic aromatic hydrocarbon molecules that can be a promising alternative class of p-type material. In the present work, DBP (Dibenzo{[f,f′]-4,4′,7,7′-tetraphenyl}diindeno[1,2,3-cd :1′,2′,3′-lm]perylene was evaluated with high bandgap as well as with mixed (FAPbI₃)_0.85(MAPbBr₃)_0.15 perovskites for the fabrication of solar cell. DBP-based solar cells yielded competitive power conversion efficiencies as compared with classical HTMs.

Abstract

We have prepared a series of Mo/ZSM-5 systems by impregnation method with different metal loading. The optimum performance has been attained for 4% metal loading, yielding to ca. 2 mmol(benzene)/g(ca)(t) at the end of the reaction. The obtained catalysts were widely structural and surface characterized. As Mo content increases, the surface feature of the support is affected specially its mesoporosity. It has been stated the enormous complexity of Mo species present in the studied system. In situ characterization by XPS reveals different reduction and carburization behaviour depending on the Mo content.

Abstract

This Special Issue contains a series of reviews and papers representing some recent results and some exciting perspectives focused on advanced strategies in thin films growth, thin films engineering by magnetron sputtering and related techniques. Innovative fundamental and applied research studies are then reported, emphasizing correlations between structuration process parameters, new ideas and approaches for thin films engineering and resulting properties of as-deposited coatings.

Abstract

The properties of ZnO based materials for ethanol detection have been studied. Cu doped samples obtained from different precursors have been investigated. ZnO and ZnS have been used as host and Cu and CuO as dopant sources.

The sensing measurements have been mostly performed at room temperature. To monitor the effect of the presence of gas, resistivity and photoluminescence experiments with and without sensing gas have been carried out. The sensing behaviour is affected by the nature of the precursors used. For ZnO:Cu and ZnO:CuO series, a higher sensitivity is obtained at the lower gas concentrations, the better response is obtained for the sample ZnO:Cu with wt.1% of metallic copper. Strong segregation effects observed in these samples could be deleterious for the sensing properties. In the series ZnS:CuO, no segregation is observed, however the sensing behaviour is erratic and attributed to the reduction of Cu ions to the metallic state.

Abstract

Mineral trioxide aggregate (MTA) is considered a bioactive endodontic material, which promotes natural mineralization at the material-tooth tissue interface. MTA Repair HP stands out because of the short setting time and the quick and effective bioactive response in vitro. The bioactivity, depens on material composition and microstructure. This work is devoted to analyze MTA Repair HP microstructural features, of both the powder precursor and set material, to get insights into the material physicochemical parameters-functionality performance relationships. Transmission electron microscopy (TEM), and field emission gun scanning electron microscopy (FEG-SEM) coupled with energy-dispersive X-ray (EDX) analyses were performed. X-ray diffraction (XRD) measurements were carried out at different times to investigate setting process. Bioactivity evaluation in vitro was carried out by soaking the processed cement disk in simulated body fluid (SBF). The presented results point out those MTA Repair HP precursor material characteristics of tricalcium silicate particles of nanometric size and high aspect ratio, which provide an elevated surface area and maximized components dispersion of calcium silicate and very reactive calcium aluminate. The MTA Repair HP precursor powder nanostructure and formulation, allows a hydration process comprising silicate hydrate structures, which are very effective to achieve both fast setting and efficient bioactive response.

Abstract

The aim of our study is to evaluate different implant surface treatments using TiIV and TiV in in vitro and in vivo studies. An in vitro study was established comprising four study groups with treated and untreated TiIV titanium discs (TiIVT and TiIVNT) and treated and untreated TiV titanium discs (TiVT and TiVNT). The surface treatment consisted in a grit blasting treatment with alumina and double acid passivation to modify surface roughness. The surface chemical composition and the surface microstructure of the samples were analyzed. The titanium discs were subjected to cell cultures to determine cell adhesion and proliferation of osteoblasts on them. The in vivo study was carried out on the tibia of three New Zealand rabbits in which 18 implants divided into three experimental groups were placed (TiIVT, TiIVNT, and TiVT). Micro-computed tomography (micro-CT) was performed to determine bone density around the implants. The results showed that cell culture had minor adhesion and cell proliferation in TiIVT and TiVT within the first 6 and 24 h. However, no differences were found after 48 h. No statistically significant differences were found in the in vivo micro-CT and histological study; however, there was a positive trend in bone formation in the groups with a treated surface. Conclusions: All groups showed a similar response to in vitro cell proliferation cultures after 48 h. No statistically significant differences were found in the in vivo micro-CT and histological study

Abstract

The growth of lead halide perovskites within metal-oxide nanoporous films has been recently considered as a means to obtain chemically and photostable ligand-free high-quality nanocrystals (NCs). The growth process, governed by the reactions taking place in nanoreactors dictated by the matrix pore size, has not been explored so far. In this work, we use photoluminescence as a tool to monitor the growth of perovskite NCs within the void network of an optically transparent matrix. We consider the effect of different external factors, such as temperature, light illumination, or precursor concentration, on the growth dynamics, and discuss a possible formation mechanism of the confined perovskite NCs. Based on this analysis, guidelines that could serve to improve the fabrication and optoelectronic quality of this type of NCs are also proposed.

Abstract

Surface modification of natural clay minerals with reagents containing metal chelating groups has great environmental value. The functionalization by adsorption or grafting guarantees a durable immobilization of the reactive organic groups, preventing their leaching when they are used in liquid media. The aim of this research was the designed mercapto functionalization of swelling brittle micas, Na-Mn, thorough both chemical and physical mechanisms. Na-Mn were functionalized with 2-mercaptoethylammonium (MEA), 2,3-dimercapto-1-propanol (BAL) and (3-mercaptopropyl)trimethoxysilane (MPTMS). The thiol concentration on swelling brittle micas is higher than the observed value for others adsorbents. The cation exchange reaction with MEA and one-step grafting with MPTMS in acid medium are the most efficient mercapto functionalization mechanism.

Abstract

N-Heterocyclic Thiones (NHT) proved to be efficient ligands for the stabilization of small platinum nanoparticles (1.3-1.7 nm), synthesized by decomposition of [Pt(dba)(2)], under a H-2 atmosphere, in the presence of variable sub-stoichiometric amounts of the NHT. Full characterization by means of TEM, HR-TEM, NMR, ICP, TGA and XPS have been carried out, providing information about the nature of the metal nanoparticles and the interaction of the NHT ligands to the metal surface. Importantly, DFT calculations indicate that some NHT ligands interact with the metal through the C & xe001;C double bond of the imidazole fragment in addition to the sulfur atom, thus providing additional stabilization to the nanoparticles. According to XPS, TGA and ICP techniques, the surface coverage by the ligand increases by decreasing the size of the substituents on the nitrogen atom. The platinum nanoparticles have been used as catalyst in the hydroboration of alkynes. The most active system is that with a less covered surface area lacking an interaction of the ligand by means of the C & xe001;C double bond. This catalyst hydroborates alkynes with excellent selectivities towards the monoborylated anti-Markovnikov product (vinyl-boronate) when one equiv. of borane is used. Very interestingly, aliphatic alkynes undergo a second hydroborylation process leading to the corresponding 1,1- and 1,2-diboroylated species with good selectivities towards the former.

Abstract

Electromicrofluidic (EMF) devices are used to handle and move tiny amounts of liquids by electrical actuation, including electrowetting-on-dielectric (EWOD) and dielectrophoresis (DEP). Monitoring the liquid characteristics in one of these devices requires suitable sensing transducers incorporated within the microfluidic structure. In the present work, we describe the incorporation of an optofluidic photonic transducer in an EMF device to monitor the refractive index of a liquid during its manipulation. The incorporated transducer consists of a responsive porous Bragg Microcavity (BM) deposited via physical vapor oblique angle deposition. Besides reporting the manufacturing procedure of the sensing-EMF device combining liquid handling and monitoring, the performance of the BM is verified by infiltrating several liquids dripped on its surface and comparing the responses with those of liquid droplets electrically moved from the delivery part of the chip to the BM location. This study proved that modified EMF devices can incorporate photonic structures to analyze very low liquid volumes (similar to 0.2 mu L) during its handling.

Abstract

The nano-porosity embedded into the tilted and separated nanocolumns characteristic of the microstructure of evaporated thin films at oblique angles has been critically assessed by various variants of the positron annihilation spectroscopy. This technique represents a powerful tool for the analysis of porosity, defects and internal interfaces of materials, and has been applied to different as-deposited SiO2 and TiO2 thin films as well as SiO2/TiO2 multilayers prepared by electron beam evaporation at 70 and 85 zenithal angles. It is shown that, under same deposition conditions, the concentration of internal nano-pores in SiO2 is higher than in TiO2 nanocolumns, while the situation is closer to this latter in TiO2/SiO2 multilayers. These features have been compared with the predictions of a Monte Carlo simulation of the film growth and explained by considering the influence of the chemical composition on the growth mechanism and, ultimately, on the structure of the films.

Abstract

Mesoporous silica features open and accessible pores that can intake substances from the outside. The combination of mesoporous silica with plasmonic nanostructures represents an interesting platform for an optical sensor based on the dependence of plasmonic modes on the refractive index of the medium in which metallic nanoparticles are embedded. However, so far only a limited number of plasmonic nanostructures are combined with mesoporous silica, including random dispersion of metallic nanoparticles and flat metallic thin films. In this study, we make a mesoporous silica layer on an aluminum nanocylinder array. Such plasmonic arrangements support both localized surface plasmon resonances (LSPRs) and extended modes which are the result of the hybridization of LSPRs and photonic modes extending into the mesoporous layer. We investigate in situ optical reflectance of this system under controlled pressure of isopropanol vapor. Upon exposure, the capillary condensation in the mesopores results in a gradual spectral shift of the reflectance. Our analysis demonstrates that such shifts depend largely on the nature of the modes; that is, the extended modes show larger shifts compared to localized ones. Our materials represent a useful platform for the field of environmental sensing.

Abstract

Enhancement of the main physicochemical properties of a natural bentonite was carried out by means of modifications using surfactant, reflux, microwave treatment and, subsequently, the incorporation of AlZr and AlCe species. The evolution of the main changes in each modification stage was evaluated by means of X-ray diffraction, N-2 sortometry, scanning microscopy (SEM), NH3-TPD, NH3-DRIFTS and CO adsorption at low temperature. For the evaluation of the catalytic behavior, the dehydration-dehydrogenation reactions of 2-propanol and hydro-conversion of decane were used; both of which generate, in addition, information regarding the acidic properties of the materials. The correlation of the number, type and acid strength with the catalytic behavior, allowed establishing the effect produced by both the delamination method and the nature of the incorporated cation. This generated tools that allow controlling the physicochemical properties, and more specifically, the enhancement of the acidity of new supports based on this type of natural clay mineral.