Scientific Papers in SCI

Abstract

The Ca-looping (CaL) process, based on the multicyclic carbonation/calcination of limestone derived CaO, has emerged recently as a potentially economically advantageous technology to achieve sustainable postcombustion and precombustion CO2 capture efficiencies. Yet, a drawback that hinders the efficiency of the CaL process is the drastic drop of limestone capture capacity as the number of carbonation/calcination cycles is increased. Precalcination of limestone at high temperatures for a prolonged period of time has been proposed as a potential technique to reactivate the sorbent, which is however precluded by regeneration temperatures above 850 degrees C and low CO2 concentrations in the carbonator to be found in the practical situation. Under these conditions, heat pretreatment leads to a stable yet very small CaO conversion. On the other hand, the introduction of a recarbonation stage between the ordinary carbonation and calcination stages has been shown to decelerate the rate of sorbent activity decay even though this favorable effect is not noticeable up to a number of above 10-15 cycles. The present manuscript demonstrates that the synergetic action of heat pretreatment and recarbonation yields a high and stable value for the multicyclic conversion of limestone derived CaO. It is foreseen that recarbonation of heat pretreated limestone would lead to a reduction of process costs especially in the case of precombustion applications. Even though sorbent purging will always be needed because of ash accumulation and sul-phation in postcombustion CO2 capture applications, the stable and high multicyclic CaO conversion achieved by the combination of these techniques would make it necessary to a lesser extent.

Abstract

Facile synthesis routes have been developed for the preparation of uniform cubic bismuth fluoride and bismuth oxyfluoride particles. The synthesis methods are based on homogeneous precipitation reactions at 120 °C in solutions of bismuth nitrate and sodium tetrafluoroborate precursors in polyol-based solvents. Both the nature of the solvent and the heating modes (conventional or microwave-assisted heating) have a remarkable effect on the morphology and crystallinity of the resulting particles. Thus, polycrystalline spheres of α-BiF3 with a mean diameter ranging from 1.2 to 2 μm could be obtained by heating solutions with the appropriate reagent concentrations in a mixture of ethylene glycol and glycerol (1 : 1 by volume) using a conventional oven, whereas octahedral single crystals of α-BiOyF3−2y with mean edges ranging from 250 nm to 920 nm precipitated when using a diethylene glycol–water mixture (8 : 2 in volume) as solvent and a microwave reactor for heating. To explain these different morphological and structural features, the mechanism of formation of such particles was investigated. Both kinds of particles were also doped with Eu3+, and both the morphological and luminescence properties of the resulting materials were evaluated. It was found that the luminescence intensity of the europium-doped α-BiOyF3−2y nanoparticles was higher than that of the europium-doped α-BiF3 sub-micrometric spheres, which was associated with the higher crystallinity of the former. Moreover, the presence of oxygen in the europium-doped α-BiOyF3−2y samples permits the excitation of the europium cations through an Eu–O energy transfer process, which results in a much higher luminescence intensity with respect to that corresponding to the direct excitation of the europium cations. Finally, the effect of the amount of dopant on the luminescence properties of the phosphors was also evaluated.

Abstract

ZnO is an attractive material for applications in dye-sensitized solar cells and related devices. This material has excellent electron-transport properties in the bulk but its electron diffusion coefficient is much smaller in mesoporous films. In this work the electron-transport properties of two different kinds of dye-sensitized ZnO nanostructures are investigated by small-perturbation electrochemical techniques. For nanoparticulate ZnO photoanodes prepared via a wet-chemistry technique, the diffusion coefficient is found to reproduce the typical behavior predicted by the multiple-trapping and the hopping models, with an exponential increase with respect to the applied bias. In contrast, in ZnO nanostructured thin films of controlled texture and crystallinity prepared via a plasma chemical vapor deposition method, the diffusion coefficient is found to be independent of the electrochemical bias. This observation suggests a different transport mechanism not controlled by trapping and electron accumulation. In spite of the quite different transport features, the recombination kinetics, the electron-collection efficiency and the photoconversion efficiency are very similar for both kinds of photoanodes, an observation that indicates that surface properties rather than electron transport is the main efficiency-determining factor in solar cells based on ZnO nanostructured photoanodes.

Abstract

H2 production from methanol/water photo-splitting was compared using various commercial photocatalysts (Evonik P25 (P25), Hombikat UV-100 (HB) and Kronos vlp7000 (KR)) and others synthesised with a sol–gel-hydrothermal (HT) process and a sol–gel method followed by calcination (SG400 and SG750). All photocatalysts had been surface modified with Au at different concentrations, from 0.2 to 6.0 wt.%, using the photodeposition method. A complete characterisation study of the different photocatalysts was performed (BET, XRD, TEM, SEM-EDX, FTIR, UV–vis Reflectance Diffuse Spectra and aggregate size). The experiments were conducted for 3.5 h using 1 g L−1 of photocatalyst with methanol (25 vol.%) as sacrificial agent. In addition to H2 generation, production of the main intermediates, formaldehyde and formic acid, and of CO2 was also evaluated. The commercial photocatalyst KR at 0.8 wt.% Au had the highest H2 production of all the photocatalysts studied with 1542.9 μmol h−1. Of the photocatalysts synthesised by our group, SG750 at Au loading of 2.0 wt.% gave the highest H2 production of 723.1 μmol h−1. The SG750 photocatalyst at Au loading of 2.0 wt.% also had the highest H2 production yield per unit of surface area at 45.5 μmol g h−1 m−2.

Abstract

Experimental catalytic activity measurements, Diffuse Reflectance Infrared Fourier Spectroscopy, and Density Functional Theory calculations are used to investigate the role and dynamics of surface oxygen vacancies in the CO oxidation with O2 catalyzed by Au nanoparticles supported on a Y-doped TiO2 catalyst. Catalytic activity measurements show that the CO conversion is improved in a second cycle of reaction if the reactive flow is composed by CO and O2 (and inert) while if water is present in the flow, the catalyst shows a similar behaviour in two successive cycles. DRIFTS-MS studies indicate the occurrence of two simultaneous phenomena during the first cycle in dry conditions: the surface is dehydroxylated and a band at 2194 cm-1 increases (proportionally to the number of surface oxygen vacancies). Theoretical calculations were conducted in order to explain these observations. On one hand, the calculations show that there is a competition between gold nanoparticles and OH to occupy the surface oxygen vacancies and that the adsorption energy of gold on these sites increases as the surface is being dehydroxylated. On another hand, these results evidence that a strong electronic transfer from the surface to the O2 molecule is produced after its adsorption on the Au/TiO2 perimeter interface (activation step), leaving the gold particle in a high oxidation state. This explains the appearance of a band at a wavenumber unusually high for the CO adsorbed on oxidized gold particles (2194 cm-1) when O2 is present in the reactive flow. These simultaneous phenomena indicate that a gold redispersion on the surface occurs under reactive flow in dry conditions generating small gold particles very actives at low temperature. This fact is notably favoured by the presence of surface oxygen vacancies that improve the surface dynamics. The obtained results suggest that the reaction mechanism proceeds through the formation of a peroxo-like complex formed after the electronic transfer from the surface to the gas molecule.

Abstract

ZnO thin films having a nanocolumnar microstructure are grown by plasma-enhanced chemical vapor deposition at 423 K on pre-treated fluorine-doped tin oxide (FTO) substrates. The films consist of c-axis-oriented wurtzite ZnO nanocolumns with well-defined microstructure and crystallinity. By sensitizing CH3NH3PbI3 on these photoanodes a power conversion of 4.8 % is obtained for solid-state solar cells. Poly(triarylamine) is found to be less effective when used as the hole-transport material, compared to 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD), while the higher annealing temperature of the perovskite leads to a better infiltration in the nanocolumnar structure and an enhancement of the cell efficiency.

Abstract

In this work, a study for understanding the role played by [ClBmim], [BF4Bmim], [PF6Bmim], and [CH3SO3Bmim] ionic liquids (ILs) in the synthesis of zeolites is presented. The use of [ClBmim] and [CH3SO3Bmim] ILs, as reported earlier [ Chem. Eur. J. 2013, 19, 2122] led to the formation of MFI or BEA type zeolites. Contrary, [BF4Bmim] and [PF6Bmim] ILs did not succeed in organizing the Si–Al network into a zeolite structure. To try to explain these results, a series of quantum mechanical calculations considering monomers ([XBmim]) and dimers ([XBmim]2) by themselves and plus cosolvent (water or ethanol) were carried out, where X ≡ Cl–, BF4–, PF6–, or CH3SO3–. Our attention was focused on the similarities and differences among the two types of cosolvents and the relation between the structure and the multiple factors defining the interactions among the ILs and the cosolvent. Although a specific pattern based on local structures explaining the different behavior of these ILs as a zeolite structuring template was not found, the calculated interaction energies involving the Cl– and CH3SO3– anions were very close and larger than those for BF4– and PF6– species. These differences in energy can be used as an argument to describe their different behavior as structure directing agents. Moreover, the topology of the cosolvent is also an ingredient to take into account for a proper understanding of the results.

Abstract

This paper presents in a comprehensive way the thermal behavior of natural and hot-washed sisal fibers, based on the fundamental components of lignocellulosic materials: cellulose, xylan and lignin. The research highlights the influence exerted on the thermal stability of sisal fibers by other constituents such as non-cellulosic polysaccharides (NCP) and mineral matter.

Thermal changes were investigated by thermal X-ray diffraction (TXRD), analyzing the crystallinity index (%Ic) of cellulosic samples, and by simultaneous thermogravimetric and differential thermal analysis coupled with Fourier-transformed infrared spectrometry (TG/DTA-FTIR), which allowed to examine the evolution of the main volatile compounds evolved during the degradation under inert and oxidizing atmospheres. The work demonstrates the potential of this technique to elucidate different steps during the thermal decomposition of sisal, providing extensible results to other lignocellulosic fibers, through the analysis of the evolution of CO2, CO, H2O, CH4, acetic acid, formic acid, methanol, formaldehyde and 2-butanone, and comparing it with the volatile products from pyrolysis of the biomass components. The hydroxyacetaldehyde detected during pyrolysis of sisal is indicative of an alternative route to that of levoglucosan, generated during cellulose pyrolysis.

Hot-washing at 75 °C mostly extracts non-cellulosic components of low decomposition temperature, and reduces the range of temperature in which sisal decomposition occurs, causing a retard in the pyrolysis stage and increasing TbNCP and TbCEL, temperatures at the maximum mass loss rate of non-cellulosic polysaccharides and cellulose decompositions, respectively. However, enriching sisal fibers in cellulose produces a decrease of TbCEL under an oxidizing atmosphere, and furthermore, a delay of the combustion process, displacing TbCOM to higher temperatures.

The results and findings of the paper would help further understanding of thermal processes where Agave fibers are involved, as the decomposition of their composites.

Abstract

An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of nanocomposites, composed of poly(lactic acid) (PLA) and organo-modified montmorillonite (OMMT) nanoparticles. This improvement has consisted of replacing the n-order conversion function by a modified form of the Sestak–Berggren equation f(α) = c (1 − α)nαm that led to a better adjustment of experimental data and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential and isoconversional methods. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function f(α) = L (L − 1)x(1 − x)L−1, corresponding to a random scission mechanism, has been tested. Once optimized the kinetic model, the thermal degradation kinetics of nanocomposites (0.5 and 2.5% of OMMT) was compared to that of the polymer matrix. Moreover, the thermal stability of nanocomposites was tested and compared to that of the polymer matrix.

Abstract

Nanocrystalline zirconium diboride (ZrB2) powder was produced by mechanochemistry from the magnesiothermic reduction in the Mg/ZrO2/B2O3 system. The use of high-energy milling conditions was essential to induce a mechanically induced self-sustaining reaction (MSR) and significantly reduce the milling time required for complete conversion. Under these conditions, it was found that the ignition time for ZrB2 formation was only about a few minutes. In this study, the mechanism for the formation of ZrB2 in this system was determined by studying the relevant sub-reactions, the effect of stoichiometry, and the thermal behavior of the system.

Abstract

Synthesis of Na-Mica-4 has been achieved by a “mix and calcine” method using sodalite and magnesium fluoride as the only precursors. Previous research found sodalite as a key intermediate reaction product in the formation of Na-Mica-4 when the NaCl melt method was employed. Similarities in structure, chemical composition and cation distribution in products using the proposed method and the NaCl melt method are described and suggest that Na-Mica-4 is a very stable product. The use of sodalite as precursor provokes microporous formation in the final mica. The absence of excess Na leads to a lower particle size and to the presence of less impurity in the calcined product. Different sodalites could be used in the synthesis of different Na-Mica-4 with presumably different physicochemical properties.

Abstract

TiBC coatings with different phase compositions (nanocrystalline TiBxCy or TiB2 phases mixed or not with amorphous carbon, a-C) were prepared by magnetron sputtering. These coatings were comparatively studied in terms of phase stability after thermal annealing at 250, 500, 750, and 1000 °C in argon using Raman and x-ray absorption near-edge spectroscopy techniques. The main differences were observed at temperatures above 500 °C when oxidation processes occur and the mechanical properties deteriorate. At 1000 °C, the samples were fully oxidized forming a-C, TiO2, and B2O3 as final products. Higher hardness and reduced indentation modulus values and better tribological properties were observed at 750 °C for nanocomposite structures including amorphous carbon and ternary TiBxCy phases. This behavior is attributed to a protective effect associated with the a-C phase which is achieved by the encapsulation of the nanocrystals in the coating and the better hard/lubricant phase ratio associated with this type of coating.

Abstract

The mechanical strength of three WC-Co grades was determined and compared under uniaxial and biaxial bending. Uniaxial four-point bending was conducted on bar-shaped specimens; biaxial testing was performed on discs using the ball-on-three-balls (B3B) method. Strength results were analysed within the frame of the Weibull theory. Differences in characteristic strength between uniaxial and biaxial bending were explained as an effect of the effective surface tested in each case. A higher Weibull modulus was obtained in one grade, independent of the testing method, which was related to its higher fracture toughness. The use and validity of the B3B biaxial test to determine the strength distribution of cemented carbides is discussed.

Abstract

Highly fluorinated polymeric (CFX), fluorine containing diamond-like carbon (F-DLC) and, for comparison, diamond-like carbon (DLC) films have been plasma deposited in a RF parallel plate reactor by using c-C4F8 as fluorine precursor and different mixtures of argon, C2H2, and H2. Plasmas have been characterized by optical emission spectroscopy, mass spectrometry, and Langmuir probe measurements. Differences in the film composition and structure have been related with the type of species formed in the plasma and with the self-bias potential developed at the deposition electrode. Additional experiments using CF4 have confirmed that the formation in the plasmas of neutral or ionized CxFy species with x > 2 is a critical factor for the synthesis of fluorine rich films.

Abstract

We design a fully stable numerical solution of the Maxwell's equations with the transfer matrix method (TMM) to understand the interaction between an electromagnetic field and a finite, one-dimensional, non-periodic structure. Such an exact solution can be tailored from a conventional solution by choosing an adequate transformation between its reference systems, which induces a mapping between its associated TMMs. The paper demonstrates theoretically the numerical stability of the TMM for the exact solution within the framework of Maxwell's equations, but the same formalism can efficiently be applied to resolve other classical or quantum linear wave-propagation interaction in one, two, and three dimensions. This is because the formalism is exclusively built up for an in depth analysis of the TMM's symmetries.

Abstract

In this study, spinodal decomposition and precipitation mechanism of mechanically alloyed supersaturated Cu–3wt.%Cr and Cu–5wt.%Cr solid solutions was investigated under nonisothermal aging. Decomposition mechanism and kinetics were studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. Also, the microstructure was characterized by transmission electron microscopy (TEM). Effect of Al2O3 reinforcement on the aging kinetics was also evaluated. It was found that Cu–3wt.%Cr and Cu–5wt.%Cr solid solutions undergo spinodal decomposition at initial stages of ageing. However, decomposition mechanism was changed to nucleation and growth by the aging progress. The aging kinetics for the Cu–Cr/Al2O3 composition appeared to be slightly faster than that for Cu–Cr, since the ageing activation energy is decreased in presence of Al2O3 nano-particles. This behavior is probably due to the higher dislocation density and other structural defects previously produced during ball milling. A detailed comparison of the DSC results with those obtained by TEM, showing good consistency, has been presented. The average size of Cr-rich precipitates was about 10 nm in the copper matrix.

Abstract

Hydrogen produced from the conversion of hydrocarbons or alcohols contains variable amounts of CO that should be removed for some applications such as feeding low-temperature polymer electrolyte membrane fuel cells (PEMFCs). The CO preferential oxidation reaction (PROX) is particularly well-suited for hydrogen purification for portable and on-board applications. In this work, the synthesis and characterization by XRF, BET, XRD, Raman spectroscopy and H2-TPR of a gold catalyst supported on a copper−cerium mixed oxide (AuCeCu) for the PROX reaction are presented. The comparison of this catalyst with the copper–cerium mixed oxide (CeCu) revealed that the experimental procedure used for the deposition of gold gave rise to the loss of reducible material by copper lixiviation. However, the AuCeCu solid was more active for CO oxidation at low temperature. A kinetic study has been carried over the AuCeCu catalyst for the PROX reaction and compared with that of the CeCu catalyst. The main difference between the models affected the contribution of the CO adsorption term. This fact may be related to the surface electronic activity produced by the interaction of the cationic species in the AuCeCu solid, able to create more active sites for the CO adsorption and activation in the presence of gold.

Abstract

Several catalytic systems containing Ni/Mg/Al/Ce were synthesized from nitrates of Ni2+, Mg2+, Al3+ and Ce3+ cations with M2+/M3+ = 2 ratios by means of the carbonate co-precipitation method and subsequent calcination at 800 A degrees C. Atomic absorption spectroscopy, X-ray diffraction (XRD), FT-IR spectroscopy, BET, temperature programmed reduction and scanning electron microscopy were used in order to describe the structural, morphological and surface characteristics of the solids completely. The effect of substitution/incorporation of Al by Ce and/or Mg on NiAl sample was studied. XRD analyses confirm that on Al-containing samples (NiAl, NiMgAl), the formation of the precursors layered double hydroxide structure. On the other hand, on cerium containing samples (NiCe, NiMgCe), poorly resolved diffractograms were observed what can be explained by the large radius of cerium. The catalysts were evaluated in the reaction of CO2 reforming of methane at 750 A degrees C. NiCe and NiMgAl catalysts exhibit higher activity and a H-2/CO ratio of almost 1. NiAl and NiMgCe samples showed lower conversions and a CH4/CO2 ratio < 1, indicating the occurrence of reverse water gas shift reaction.

Abstract

A combination of transmission electron microscopy techniques and spatially resolved microanalysis is used to investigate the nanostructure, constituting phases, and chemical elemental distribution in CrAlYN multilayered coatings. The location of the metallic elements and their chemical state are needed to understand their functional properties. Samples were prepared with variable Al (4-12 at%) and Y (2-5 at%) contents by direct current reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N-2 mixtures under different deposition parameters (power applied to the target and rotation speed of the sample holder). The changes produced in the nanostructure and chemical distribution were investigated. Nanoscale resolution electron microscopy analysis has shown that these coatings present a singular nanostructure formed by multilayers containing at a certain periodicity nanovoids filled with molecular nitrogen. Spatially resolved energy dispersive spectroscopy and electron energy loss elemental mappings and profiles showed that the chromium, aluminum, and yttrium atoms are distributed in a sequential way following the position of the targets inside the deposition chamber. Analysis of the different atomic distribution and phases formed at the nanoscale is discussed depending on the deposition parameters.

Abstract

This work reports the low temperature plasma formation of Ag@TiO2 nanorods (NRs) on processable substrates. The layers have been analyzed by electron microscopy and secondary ion mass spectroscopy. The NRs morphologies suggest that the plasma sheath, the high mobility of the silver and the incoming direction of the precursor moieties are key factors determining their shape, dimensions, and tilting orientation. Both amorphous and anatase Ag@TiO2 NRs surfaces are superhydrophobic, and turn into superhydrophilic by irradiation with UV light. This wetting behavior is discussed by considering the water penetration in the inter-NR space during the light-mediated transformation.

Abstract

Bone loss is still a major problem in orthopedics. The purpose of this experimental study is to evaluate the safety and regenerative potential of a new scaffold based on a bio-ceramization process for bone regeneration in long diaphyseal defects in a sheep model. The scaffold was obtained by transformation of wood pieces into porous biomorphic silicon carbide (BioSiC®). The process enabled the maintenance of the original wood microstructure, thus exhibiting hierarchically organized porosity and high mechanical strength. To improve cell adhesion and osseointegration, the external surface of the hollow cylinder was made more bioactive by electrodeposition of a uniform layer of collagen fibers that were mineralized with biomimetic hydroxyapatite, whereas the internal part was filled with a bio-hybrid HA/collagen composite. The final scaffold was then implanted in the metatarsus of 15 crossbred (Merinos-Sarda) adult sheep, divided into 3 groups: scaffold alone, scaffold with platelet-rich plasma (PRP) augmentation, and scaffold with bone marrow stromal cells (BMSCs) added during implantation. Radiological analysis was performed at 4, 8, 12 weeks, and 4 months, when animals were sacrificed for the final radiological, histological, and histomorphometric evaluation. In all tested treatments, these analyses highlighted the presence of newly formed bone at the bone scaffolds' interface. Although a lack of substantial effect of PRP was demonstrated, the scaffold+BMSC augmentation showed the highest value of bone-to-implant contact and new bone growth inside the scaffold. The findings of this study suggest the potential of bio-ceramization processes applied to vegetable hierarchical structures for the production of wood-derived bone scaffolds, and document a suitable augmentation procedure in enhancing bone regeneration, particularly when combined with BMSCs.

Abstract

CdSe@ZnS nanocomposites have been prepared by a two-step solid state mechanochemical synthesis. CdSe prepared from Cd and Se elements in the first step was mixed with zinc acetate and sodium sulphide in the second step of milling to prepare a CdSe@ZnS nanocomposite. In the third step, the obtained nanocomposite was coated with l-cysteine to prepare a biocompatible system. The crystallite size of the new type of nanocomposite was 20–35 nm for cubic CdSe and 3–8 nm for hexagonal ZnS as calculated from XRD, TEM and SEM data. The synthesised samples show good crystallinity and have been tested for dissolution and cytotoxicity. The dissolution of cadmium from CdSe@ZnS was less than 0.05 μg mL−1, whereas a value of 0.8 μg mL−1 was measured for CdSe alone. The binding of ZnS with CdSe in the nanocomposite practically eliminated the release of cadmium into solution. As a consequence, a very low cytotoxic activity has been evidenced for CdSe@ZnS. The nanocomposites coated with l-cysteine have a great potential as fluorescent labels in biomedical engineering.

Abstract

High charged swelling micas, with layer charge between 2 and 4, have been found to readily swell with water, and complete cation exchange (CEC) can be achieved. Because of their high CEC, applications like radioactive cation fixation or removal of heavy metal cations from wastewater were proposed. Their applicability can be controlled by the location of the interlayer cation in a confined space with a high electric field. In synthetic brittle micas, the interlayer cation has a low water coordination number; therefore, their coordination sphere would be completed by the basal oxygen of the tetrahedral layer as inner-sphere complexes (ISC). However, no direct evidence of these complexes formation in brittle micas has been reported yet. In this contribution, we mainly focus on the understanding the mechanisms that provoke the formation of ISC in high charge swelling micas, Mica-n. A whole series of cations (X) were used to explore the influence of the charge and size of the interlayer cation. Three brittle swelling micas, Mica-n (n = 4, 3 and 2), were selected in order to analyze the influence of the layer charge in the formation of ISC. The contribution of the ISC has been analyzed thorough the evolution of the 060 reflection and the changes in the short-range order of the tetrahedral cations will be followed 29Si and 27Al MAS NMR. The results showed that ISC was favored in X-Mica-4 and that provoked a high distortion angle between the Si–Al tetrahedra. When the content of aluminum decreases, the electrostatic forces between the layers are relaxed, and the hydrated cations did not interact so strongly with the tetrahedral sheet, having the opportunity to complete their hydration sphere.

Abstract

Pt-TiO2/g-C3N4-MnOx hybrid structures are synthesized by means of a simple impregnation method of Pt-TiO2 and g-C3N4-MnOx. From the wide structural and surface characterization we have stated that TiO2/g-C3N4 composites are formed by an effective covering of g-C3N4 by TiO2. The modification of composite by Pt and/or MnOx leads to improved photoactivities for phenol degradation reaction. Moreover, enhanced photoactivities have been obtained for composites systems for H2 evolution reaction. The notably photocatalytic performance obtained was related with the efficient separation of charge pairs in this hybrid heterostructure.

Abstract

The one-step preparation of silver nanoparticles and dendritic structures mediated by aqueous royal jelly solutions has been investigated for the first time. It has been found that royal jelly (RJ) is a complex organic matrix that can be simultaneously used as a reducing and stabilizing agent in the chemical synthesis of colloidal silver-based nanostructures from aqueous AgNO3 solutions, without the requirement of additional reagents or heating sources to initiate the oxidation–reduction reactions. The resulting product consisted of very fine single-crystal disks of Ag and silver 4,4′-dimethyldiazoaminobenzene (a triazenic compound). Both kinds of particles tended to coalesce and form supramolecular dendritic structures, the AgNO3/RJ weight ratio chosen in the synthesis being a key parameter to control the crystal growth and the microstructural properties of the Ag nanodisks. Data obtained from Fourier transform infrared and Raman spectroscopy analysis indicated that these nanostructures are coated by RJ biomolecules (residues of proteins and carbohydrates). In vitro biological assays showed that these nanostructures exhibit a promising enhanced antibacterial activity against both Gram-positive and Gram-negative bacteria.

Abstract

The tribological properties of CrAlN, CrAlYN and CrAlZrN coatings deposited by direct current reactive magnetron sputtering are studied by means of pin-on-disc experiments at room temperature, 300, 500 and 650 °C using alumina balls as counterparts. The influence of the metallic composition (Al, Y and Zr) on the friction, wear properties and oxidation resistance is studied by means of scanning electron microscopy, energy dispersive X-ray analysis and Raman analysis of the contact region after the friction tests. The results obtained allow us to classify the tribological behaviour of the CrAl(Y,Zr)N coatings into three groups according to the nature of the dopant and aluminium content. The sliding wear mechanism is characterized by the formation of an overcoat rich in chromium and aluminium oxides whose particular composition is determined by the initial chemical characteristics of the coating and the testing temperature. The fraction of Cr2O3 becomes more significant as the Al content decreases and the temperature increases. The addition of Y, and particularly Zr, favours the preferential formation of Cr2O3 versus CrO2 leading to a reduction of friction and wear of the counterpart. Conversely, the tribological behaviour of pure CrAlN coatings is characterized by higher friction but lower film wear rates as a result of higher hardness and major presence of aluminium oxides on the coating surface.

Abstract

The framework to describe the out-of-equilibrium free electrons in cold plasmas is developed assuming the electron entropy is defined through the Boltzmann H-theorem. Our theory explains why the Saha-Boltzmann relation among higher-lying excited states by means of the electron kinetic temperature is fulfilled, even when free electrons are far from equilibrium. The thermodynamic electron temperature, pressure and chemical potential have been introduced through the derivatives of the electron entropy. It is demonstrated that under usual conditions in cold plasmas, e.g. when the electron distribution function possesses the Maxwellian, Druyvestein or Kappa functional forms, kinetic and thermodynamic electron temperatures yield the same value.

Abstract

Aluminium and magnesium were used in the M/ZrSiO4/B2O3/C (M = Al, Mg) system to induce a mechanically induced self-sustaining reaction (MSR). Aluminium was not able to reduce the system to the desired products, and the system became amorphous after 10 h milling. However, nanocomposite powder of ZrB2–SiC–ZrC was in situ synthesized by the magnesiothermic reduction with an ignition time of approximately 6 min. The mechanism for the formation of the product in this system was determined by studying the relevant sub-reactions.