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In this work, low-Pt content nanocatalysts (≈ 5 wt. %) supported on Hollow Carbon Spheres (HCS) were synthesized by two routes: i) colloidal conventional polyol, and ii) surfactant-free Bromide Anion Exchange (BAE). The nanocatalysts were labelled as Pt/HCS-P and Pt/HCS-B for polyol and BAE, respectively. The physicochemical characterization of the nanocatalysts showed that by following both methods, a good control of chemical composition was achieved, obtaining in addition well dispersed nanoparticles of less than 3 nm TEM average particle size (d) on the HCS. Pt/HCS-B contained more Pt0 species than Pt/HCS-P, an effect of the synthesis method. In addition, the structure of the HCS remains more ordered after BAE synthesis, compared to polyol. Regarding the catalytic activity for the Oxygen Reduction Reaction (ORR) in 0.5 M KOH, Pt/HCS-P and Pt/HCS-B showed a similar performance in terms of current density (j) at 0.9 V vs. RHE than the benchmark commercial 20 wt. % Pt/C. However, Pt/HCS-P and Pt/HCS-B demonstrated a 6 and 5-fold increase in mass catalytic activity compared to Pt/C, respectively. A positive effect of the high specific surface area of the HCS and its interactions with metal nanoparticles and electrolyte, which promoted the mass transfer, increased the performance of Pt/HCS-P and Pt/HCS-B. The high catalytic activity showed by Pt/HCS-B and Pt/HCS-P for the ORR, even with a low-Pt content, make them promising cathode nanocatalysts for Anion Exchange Membrane Fuel Cells (AEMFC).

This work reports the synthesis and characterization of metal-free electrocatalysts made from Brosimum alicastrum waste as the carbon source. The residues were washed and grounded to a fine powder. The thermogravimetric analysis carried out on the raw sample showed that the optimal synthesis temperature is 700 °C. Thus, the raw sample was pyrolyzed at 700 °C and activated with potassium hydroxide (KOH) in a 2:1 ratio (KOH/fine power) to improve its properties. Afterwards, hydrazine was used as the nitrogen source for doping. The physicochemical characteristics of pyrolyzed, activated, and doped carbons were studied and their electrochemical properties were determined using cyclic and linear voltammetry techniques. The electrochemical measurements indicate that the sample doped at 140 °C has an acceptable onset potential (0.854 V vs. RHE), while the one doped at 160 °C shows the highest current density among the synthesized electrocatalysts (2.61 mA cm-2). Although the catalyst performance is lower compared to commercial 20% Pt/C, this biomass precursor favors the oxygen reduction reaction in alkaline media.

In this work a first approximation to obtain non-noble metal electrocatalysts from onion skin wastes is reported. Biocarbon were obtained at a range of 600–800 °C of pyrolysis temperature activated by chemical treatment with HNO3. It was observed that the pyrolysis temperature has a direct effect on the structural and textural properties, besides the morphology of the onion skin waste-derived biocarbon, which shows to have influence on the catalytic activity for the oxygen reduction reaction ORR. AOB700 was the non-noble metal electrocatalyst with the best performance for the ORR evaluated in alkaline electrolyte (0.5 mol L−1 KOH), which had the highest surface area (242 m2g-1) and a current density of −2.35 mA cm−2 with an onset potential of 0.82 V/RHE. The chemical surface composition shows that N-pyridinic, N-amine, N-quaternary and N-pyrrolic nitrogen species are present on this electrocatalysts. The use of onion skin waste as raw material in the production of non-noble metal electrocatalysts is a sustainable solution to avoid the disposal of abundant biomass residues as onion skins.

In this work, high surface area N-doped carbon synthesis from Sargassum spp. is reported as a low cost alternative for electrocatalysts production for the oxygen reduction reaction (ORR). First, Sargassum spp. was activated with potassium hydroxide (SKPH) and then doped with hydrazine (SKPHD). As a result of the activation process, SKPH obtained a high surface area (2289 m2 g−1), 0.16% nitrogen and 2.63% sulfur content; it also showed four-electron-transfer mechanism when tested as electrocatalyst in alkaline medium. Besides, SKPHD presented 3.60% nitrogen content in the bulk and higher ORR activity (0.838 V onset potential vs. RHE and 4.59 mA cm−2 current density) very close to 20% Pt/C (5.25 mA cm−2). Results indicate that using seaweeds as a synthesis precursor is an alternative for the Sargassum spp. disposal in the Caribbean due to its high availability and efficiency towards ORR.

Metal-free electrocatalysts for the oxygen reduction reaction (ORR) were synthesized from cassava residues through a thermal functionalization with sulfuric acid. Their electrocatalytic activities were tested through the ORR performance in basic media. Chemical composition in samples seems to play an important role in their electroactivity, more than textural properties, as the sulfur-treated high-temperature sample (Sy800) has the best performance with an onset potential of 0.69 V vs RHE (reversible hydrogen electrode) and a current of −2.32 mA cm−2 at 0.3 V vs RHE. These functionalized cassava residues are promising materials to be used like carbon-based metal-free electrocatalysts.

In this work, the synthesis and characterization of novel metal-free electrocatalysts obtained from leather scraps is reported. The waste material has been subjected to simple thermochemical treatments (pyrolysis, chemical activation and doping), obtaining high performance electrocatalysts for the Oxygen Reduction Reaction (ORR) in KOH. The effect of pyrolysis temperature on the physicochemical properties and electrochemical performance is studied. The metal-free electrocatalysts possess mesoporous structure with high specific surface area (819–2100 m 2 g −1 ). A higher catalytic activity has been determined for the electrocatalyst treated at 700 °C (AB7), compared to samples pyrolyzed at higher temperatures. Furthermore, AB7 delivers a higher current density compared with commercial 20% Pt/C (j = 9.0 and 4.5 mA cm −2 , respectively), while its on-set potential shifts only 145 mV to more negative values. The metal-free catalysts are a promising eco-friendly and scalable alternative as cathode materials for alkaline fuel cells and other electrochemical energy devices.

The process of biodeterioration is one of the main problems affecting historical monuments and buildings. On rock surfaces, different types of microorganisms establish in the most adequate niches and accelerate degradation, leading to the irreversible loss of cultural heritage. Therefore, new ways to preserve cultural heritage must be urgently studied to prevent such damage. In this study, the broad-spectrum antimicrobial activity of calcium zinc hydroxide dehydrate [Ca(Zn(OH)3)2·2H2O] (CZ) and zinc oxide (ZnO) nanoparticles synthesized by the sol–gel method is examined against fungal and bacterial model organisms. The selected microbes were inhibited by both nanoparticles, yet CZ was the most effective, with a bactericidal activity of 1.25 to 5 mg/mL and a fungicidal activity of 0.625 mg/mL. Both nanoparticles caused structural damage to the evaluated fungal cells, resulting in morphological changes and affecting the germination of conidia. For the first time in the literature, the antibacterial activity and the mode of action of CZ are reported. In conclusion, CZ nanoparticles are shown to be potential candidates for the treatment of rock surfaces of built cultural heritage., We are grateful for the financial support of the National Council for Science and Technology (Consejo Nacional de Ciencia y Tecnología [CONACyT]) of the “Fronteras de la Ciencia 138” project. Additional thanks are extended to CONACyT for the doctoral scholarship granted to MSC 282192.

The evaluation of the antifungal activity of Mg(OH)2 and Ca(OH)2 nanoparticles (NPs), synthesized by sol–gel method and their mixtures at different concentrations, is reported. The antifungal activity of the hydroxide NPs was studied using Aspergillus niger and Penicillium oxalicum isolated from stone surfaces. These model organisms were selected due to their ability to grow on outdoor and indoor climates and their significant impact on human health. Moreover, the antifungal activity of Mg(OH)2 and Ca(OH)2 NPs dispersed in positively charged polymeric matrices based on partially quaternized poly(2-(dimethylamino ethyl) methacrylate) (pDMAEMA) was studied. With respect to the morphology, particle size, and textural properties of the NPs, the mixtures of Mg–Ca hydroxides revealed a uniform and smaller particle size, along with a greater surface area, as compared to pristine Ca(OH)2 NPs. However, the Ca(OH)2 and a mixture of Mg(OH)2 and Ca(OH)2 (10:90 weight ratio) NPs, showed an enhanced growth inhibition of A. niger and P. oxalicum, suggesting that the effect of particle size on the antifungal activity would not be a preponderating factor. In addition, improved antifungal properties against A. niger and P. oxalicum were detected in composite coatings based on hydroxide NPs dispersed in quaternized p(DMAEMA-co-METAI). The use of these systems might provide promising composite materials with potential antifungal properties for various applications., This study was financially supported by the National Council for Science and Technology (Consejo Nacional de Ciencia y Tecnología [CONACYT, Mexico]) of the “Fronteras de la Ciencia No. 138” project and by the Community of Madrid under the “Climortec”, BIA2014−53911-R, “Geomaterials 2” Programme (S2013/MIT_2914), and Multimat Challenge (S2013/MIT-2862). A.S.-F. would like to gratefully acknowledge the financial support of Santander Universidades through “Becas Iberoamérica Jóvenes Profesores e Investigadores, España 2015” scholarship program. C.G.-S., R.Y.-M., and U.S.S. thank CONACYT and the Deutscher Akademischer Austauschdienst (DAAD, Germany) for financial support within the framework of the funding program for international mobility PROALMEX 2015 (CONACyT project: 267752 and DAAD project: 57271725). C.G.-S. and U.S.S. also thank the Deutsche Forschungsgemeinschaft (DFG, Germany) for financial support for this research under the scheme of the grant SFB-1278 “PolyTarget” project B02.

Mesoporous silica nanoparticles (MSNs) are frequently functionalized to be used for specific applications, including catalysis and biomedical engineering. In this research, MCM-41-MSNs were synthesized by the sol–gel method and were functionalized with different quantities of (3-aminopropyl) triethoxysilane (APTES) using a post-grafting method to determine the physicochemical and structural changes in the MSNs. The functionalized materials were assessed by different characterization techniques, namely, TGA, FTIR, BET, SEM, TEM, DLS, zeta potential, SAXS, XRD and XPS. The FTIR data confirmed the presence of amino groups on the MSN surfaces, and the results from the XPS, TGA and zeta potential demonstrated that the APTES concentration during post-grafting directly affects the quantity of amino groups bound to the MSNs. The SAXS, TEM and nitrogen adsorption–desorption analyses showed that as the amount of APTES in the MSNs increases, the mesoporous structure become more disordered.

This study presents a correlation between microstructure, atomic-scale observations and intrinsic cathodoluminescence (CL) emission from two types of brucite (Mg(OH)2) nanoparticles synthesized by hydrothermal and sol–gel methods, and a third one that was commercially acquired. It is reported, for the first time, spectral CL in an environmental scanning electron microscope, in the blue region (λ ∼300–660 nm). X-ray diffraction (XRD), environmental and field emission scanning electron microscopy (ESEM, FESEM) transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM)-electron diffraction were carried out for morpho-structural characterization. HRTEM observations allowed highlighting features at the atomic scale, including the different degrees of misfit inherent to each type of synthesis. Dislocations and stacking faults were oriented parallel to 0001 planes, giving rise to strain fields that explained the strongly preferred orientation observed by XRD in the commercial sample. In the same way, edge dislocations affected the 0001 planes of the hydrothermal sample. In the sol–gel sample, distortions produced by bent lattice planes affected the stacking sequence of 011–1 planes and confirmed the XRD results. CL showed strong dependence on particle orientation. Stable signals with peaks at 381 nm (3.25 eV), 409 nm (3.03 eV) and 466 nm (2.66 eV) were detected in the three samples along the (11–20) surface after applying 20 kV. Some differences in the intensity degree and peak position were detected in the (0001) surface. Additional signals at 425 (2.91 eV) and 488 (2.54 eV) detected in the sol–gel sample confirmed the presence of magnesite (MgCO3) due to carbonation processes. The intrinsic CL emissions were associated with differences in the development of lattice strains, which produced luminescence centers. Better understanding of intrinsic CL was achieved thanks to the correlation with microstructure and atomic-scale properties., This study was supported by the Autonomous Region Program of Madrid, Geomateriales 2 (S2013/MIT_2914), Multimat-Challenge (S2013/MIT-2862), Innovation and Education Ministry (Climortec, BIA2014-53911-R, MAT201347460-C5-5-P), MAT2016-80875-C3-3-R, S2013/MIT-2862 projects and the CONACYT project Fronteras de la Ciencia No. 138.

Microstructure and composition are factors determining heat transfer in ZnO ceramic materials, which define the performance of the material after Joule heating, generated by electron transport. In this study, photothermal radiometry was applied to investigate the influence of the sintering temperature, ranging from $$800\,{^{\circ }}\hbox {C}$$ to $$1300\,{^{\circ }}\hbox {C}$$ , by measuring the thermal diffusivity and thermal conductivity at room temperature, of commercial and sol–gel ZnO pellets. Our results show that the values of these thermal properties for both types of ZnO increase when the sintering temperature increases, displaying maximum energy dissipation at $$1200\,{^{\circ }}\hbox {C}$$ . Additionally, the role of the sintering temperature on the optical properties was also analyzed using diffuse reflectance spectroscopy, and from these data the optical band-gap was obtained.

In this work, the development of a new crystallization technique is reported, using nitrogen plasma (AC) to obtain nanostructured anatase and rutile from amorphous titanium oxide (TiO2). This methodology increases throughput and minimizes thermal effects. Nanostructured amorphous TiO2 was obtained by the sol-gel method and subsequently subjected to AC treatment, at a controlled pressure, applying different powers and treatment times in order to obtain phase changes. The obtained samples were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The results show the crystallization in parallel with anatase and rutile phases with a proportion that is directly related to the applied power in the plasma and the treatment time. This technique allows us to obtain smaller crystals in comparison with those of classic thermal methodologies. It is also demonstrated that the application of plasma represents a novel and innovative method to obtain phase polymorphic changes in titanium oxide without needing to apply prolonged heat treatments at high temperatures and can therefore be taken into consideration as a technique with low energy costs, in comparison with conventional heat treatments.

Limestone is a sedimentary rock composed of calcium carbonate with minor amounts of silica, iron oxide, clay, dolomite, and organic material. These types of stones have been used extensively as building materials. Due to this, determination of their thermal properties is of the utmost importance. These properties depend on the microstructure and composition of each type of rock. In this study, the effect of the thermal treatment of three different limestone rocks from the Peninsula of Yucatan were studied, in the range from 100 °C up to 600 °C, using photothermal radiometry. These studies were complemented by the characterization of the crystalline phases using X-ray diffraction and effective porosity measurements performed by the saturation technique. It is shown that the thermal diffusivity, thermal conductivity, and specific heat of the limestone decrease as the temperature increases. This behavior can be related to increases in microcracks and effective porosity due to thermal treatments.

Chitinous materials are common in nature and provide different functions including protection and support of many invertebrate animals. Exoskeletons in these organisms constitute the boundary regulating interaction between the animal and the external environment. For this reason, it is important to study the physical properties of these skeletons, in particular, thermal properties. The objective of this study is to investigate the thermal diffusivity of the skeletons of four species of marine invertebrates, Antipathes caribbeana (black coral), Panulinus argus (lobster), Callinectes sapidus (crab), and Limulus polyphemus (xiphosure). Thermal characterization is performed using photothermal radiometry (PTR) and laser-flash techniques. The measurements are complemented with structural characterization using X-ray diffraction. The results using both laser flash and PTR are consistent. These indicate that the thermal properties are strongly dependent on the presence of biogenic minerals (calcium and/or magnesium) and on the crystallinity index of the structure. The thermal-diffusivity values show an increase as a function of the crystallinity index.

In this work the formation of thin films by evaporation of liquid mixtures of agglomerated amorphous untreated fumed silicon dioxide nanoparticles is analyzed. Fumed silica is a material that has been used as a thickening agent due to the fact that it has chain-like particle morphology. When mixed with a liquid, the chains bond together and increase the viscosity. The experiments were performed on samples deposited on a metallic substrate. Thermal waves were generated by sending a modulated laser beam at constant frequency onto the substrate. These waves are propagated to the evaporating solution allowing the monitoring of the film formation. It is shown that the last stage of the film formation is strongly affected by the formation of cracks and migration of the material to the lateral surface of the container. The experimental data are compared with predictions of effective thermal property models.

Titanium oxide matrix was prepared by sol-gel adding fluoxetine [Prozac (C17H18NF3O)] during the reaction of gelation. This nanostructured material was studied by Fourier transform infrared (FTIR) spectroscopy, N2 adsorption, and x-ray diffraction to detect the interaction between the drug and the matrix. The complex nature of FTIR signals for the matrix and the drug did not allow observation of the interactions; however, using the density functional theory formalism, two stable complexes are suggested to be formed on the drug–matrix system. Both complexes are formed through H bond interactions involving the amine group in fluoxetine and the hydroxylated sites in titanium xerogel. They were found to be energetically stable and independent of the titanium model core cluster used in the calculations.

Silica gel and MCM-41 synthesized mesoporous materials were treated with either oxygen (O2), hexamethyldisiloxane (HMDSO) and organic vapors like ethanol (EtOH), and acrylonitrile (AN) inductive plasma. The radiofrequency power for the modification was fixed to 120 W and 30 min, assuring a high degree of organic ionization energy in the plasma. The surface properties were studied by infrared spectroscopy (FTIR), scanning electron microscopy, x-ray photoelectron spectroscopy and dynamic light scattering technique was used for characterizing size distributions. When the silica and MCM-41 particles were modified by AN and HMDSO plasma gases, the surface morphology of the particles was changed, presenting another color, size or shape. In contrast, the treatments of oxygen and EtOH did not affect the surface morphology of both particles, but increased the oxygen content at the surface bigger than the AN and HMDSO plasma treatments. In this study, we investigated the influence of different plasma treatments on changes in morphology and the chemical composition of the modified particles which render them a possible new adsorbent for utilization in sorptive extraction techniques for polar compounds.

In this work, the kinetics of diffusion of methylene blue in agar aqueous solution is studied using a photoacoustic technique. Two agar phantoms solutions in water with a relation of mass/volume of 0.01% and 0.05% were analyzed. The study was performed using a modified Rosencwaig photoacoustic cell that is enclosed by transparent windows, on both sides. The sample is deposited directly on top of the upper window. A red light beam, at a fixed modulation frequency, is sent through the lower window illuminating the sample and inducing the photoacoustic effect inside the closed chamber of the cell. At the beginning of the experiment, a droplet of 100μL of agar solution is deposited; afterwards, the signal stabilizes, and 10μL of methylene blue aqueous solution (0.0125 g · mL−1) is added to the surface of the agar. During the first seconds of the experiment, the photoacoustic signal amplitude increases followed by a gradual and long decay. Results for modulation frequencies in the range from 10Hz to 80Hz for both agar concentrations are presented. A simple theoretical approach is presented to analyze the experimental data. It is demonstrated that the kinetics of the process can be parameterized as a function of the changes of an effective optical absorption coefficient. From these results, the characteristic time, in which the dye diffusion process stabilizes, is obtained. It is found that this time is larger for samples with a higher agar concentration. These differences provide important results for biomedical sciences in which agar gels are used as phantoms resembling some of the properties of living organs and tissues.

Different fields such as archaeology, biomedicine, forensic science, and pathology involve the analysis of burned bones. In this work, the effects of successive thermal treatments on pig long bones, measured by photothermal radiometry and diffuse reflectance are reported. Measurements were complemented by X-ray diffraction and infrared spectroscopy. Samples were thermally treated for 1 h within the range of 25 °C to 350 °C. The thermal diffusivity and reflectance increase in the low-temperature range, reaching a maximum around 125 °C and decaying at higher temperatures. These results are the consequence of complex modifications occurring in the inorganic and organic bone structure. For lower temperatures dehydration, dehydroxilation, and carbonate loss processes are dominant, followed by collagen denaturing and decompositions, which have an influence on the bone microstructure.

Calcium carbonate is the most abundant inorganic material, and it was used to build the ancient Mayan monuments in the peninsula of Yucatan, Mexico. One of the most important challenges that these structures have to confront is related to water and its transport inside the stone that induces serious deterioration. In this study, the photoacoustic (PA) technique is used to monitor the water permeability of two kinds of solid and compacted powdered stones. The analysis of water permeability in stones is performed using a modified Rosencwaig PA cell. When the stones are in contact with the water reservoir, the PA signal amplitude is observed to decay gradually due to the progressive wetting of the sample. Based on this type of experiment, the water diffusion coefficients as well as the time evolution of the thermal effusivity are obtained.

Several compositions in the system TiO2-MgO were prepared via sol–gel method. The structural evolution of the samples was followed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal analysis (DTA/TG). In order to study the crystalline phase stability over time, the amorphous fresh gels were subjected to successive thermal treatments from 100 to 1100 °C, with a total annealing time of 442 h. Below 350 °C, magnesium acetates and oxalates phases were detected; at higher temperatures the binary compounds MgTi2O5, MgTiO3 and Mg2TiO4 appeared over a wide range of compositions. In the titania rich end, brookite, anatase and rutile were detected, these phases easily reacted to form the binary oxides; in contrast, on the rich-end magnesia, periclase showed an overall high stability. The successive thermal treatments over an extended period of time allowed a better control of nanosized crystallite growth; for anatase was 30 nm, below 850 °C, and for rutile was 45 nm, between 600 °C and 1000 °C. Magnesia showed a constant value of 22 nm on the overall studied temperatures. The best catalytic performance for 2-propanol decomposition was achieved by 90Ti/10Mg, annealed at 400 °C; this indicates that when magnesium is added to titania, the catalytic activity improves due to the introduction of structural defects and charge deficiencies. For 2-butanol decomposition, the formation of cis and trans isomers indicates the presence of high acidity sites.

Aqueous solutions of agar show a sol–gel transition temperature in the range from 32°C to 47°C depending on colloid concentration; however, the width of the transition and the subsequent process occurring after it, are not well understood. In this work the sol–gel transition of agar is studied by a simple optical method. It consists of the illumination of the sample using a non-coherent light source and the monitoring of transmitted light using a photodiode. It is shown that during the sol–gel transition, the transmitted light decays over a broad range of temperature. Simultaneously, it is possible to observe that fluctuations in the transmitted light decrease along the sol–gel transition, and at a specific temperature, they become very small. Based on these observations, the sol–gel transition temperature for three different concentrations of agar (0.5, 1.5, and 2.5% w/v) is determined. These results are compared with the sol–gel transition temperature values provided by the conventional rheological method.

Calcium oxide and a mixed CaO(10)–SiO2(90) wt% sample were synthesized by sol–gel method, using HCl or HNO3 as hydrolysis catalysts. The powders were thermally treated at 200, 400, 600 and 800 °C. Sample characterization was carried out by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The specific surface area and pore volume were measured by the BET method. For the pure samples, it was found that the crystalline phases and structural properties depend on the catalyst used during the synthesis; whereas the surface areas were similar in both cases. On the other hand, at high temperatures, the mixed CaO–SiO2 oxide showed glass-like properties, where CaO is dispersed in an amorphous phase.

Sodium phenytoin, C15H11N2NaO2, in several concentrations was co-gelled with titania (TiO2), by a sol–gel process. This technique is a promising method to encapsulate several drugs, in this case, phenytoin is an anticonvulsant used to control epileptic seizures. Samples were prepared by adding different concentrations (X = 50, 100, 200 and 250 mg per 20 g of titania matrix) of sodium phenytoin (Ph) to a solution of titanium n-butoxide. The resulting titania–Ph-X materials were characterized by transmission electron microscopy (TEM), Fourier transformed infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and Brunauer–Emmet–Teller (BET) surface areas. The porous nanomaterials showed a wide range of particle size, from 10 to 210 nm, with a mean pore diameter of 5 nm. X-ray diffraction showed an amorphous structure of the prepared samples.

Groundwater pollution by nitrates is a widespread problem in many locations in the world. The underground aquatic mantle of the Peninsula of Yucatan is highly vulnerable due to its karstic nature. Adsorption methods are a good choice for nitrate elimination. In this work, a natural calcium bentonitewas modified by acid thermoactivation with HCl and H2SO4, and tested as a media for nitrate removal in an aqueous solution. The nitrate concentration in the solution was measured by FT-IR, using the Lambert‐Beer law. Clay characterization was carried out by X-ray diffraction and FT-IR spectroscopy; surface area was measured by the BET method.

Agar films were subjected to natural weathering exposure in a humid tropical climate for 90 days to determine their biodegradation behavior and functionality. Exposed samples were taken at 15, 30, 45, 60 and 90 days. Mechanical, thermal, structural and morphological properties were determined using tensile test, differential scanning calorimetry (DSC), attenuated reflectance infrared spectroscopy (ATR-FTIR), X-ray diffraction and environmental scanning electron microscopy (ESEM). The photodegradation process and temperature–relative humidity fluctuations promoted a decrease in agar mechanical properties in early exposure stages (30–45 days) caused by a reduction in agar molecular size and a decrease in the number of sulfate groups. These changes alter agar crystallinity, causing contraction that leads to formation of micro-fractures and embrittlement, and promote microbial attack. Accelerated weathering exposure of agar films showed that outdoor climate parameters play an important role in their degradation. These results will aid in further research to determine the potential use of agar as an environmentally friendly solution to the problem of biodegradable composites disposal.

Tin oxide films deposited on glass substrates were prepared using a metallic tin target in a DC-magnetron sputtering system. Pure oxygen (99.9%) was used as oxidant and plasma gas. The experiments were carried out at a fixed current mode of the power supply and the cathode voltage was measured during 15 min, the first 5 min of pre-sputtering and the last 10 were used for film growth. The deposition was carried out under different conditions of current, oxygen pressure and substrate temperature. The crystalline phases present in the films were identified with an X-ray diffractometer, equipped with a grazing incidence attachment. The angle of incidence was 3°. The preferred orientation degree in the tin oxide films and the relative cassiterite (SnO 2 ) proportion for each reflection were calculated from the deconvoluted X-ray peaks. It was found that the synthesis conditions have a strong influence over the growth texture and the relative cassiterite proportion over romarchite formation (SnO). To obtain tin oxide films with a high SnO 2 proportion and a high texture in reactive oxygen sputtering, were necessary, relatively high values of substrate temperature, current and oxygen pressure.

Several compositions in the CaO-ZrO2 system were synthesized from zirconium n-butoxide and calcium methoxide, by the sol-gel method. Hydrolysis and gelation occurred at pH 3, using H2SO4 as hydrolysis catalyst. Fresh gels were annealed in air at 100 to 900°C, in 100°C steps every 20 h, for a total annealing time of 140 h. Analysis by X-ray diffraction showed the formation of hydrated calcium sulfate together with amorphous zirconia up to 400°C. At the ZrO2 rich-end, tetragonal and monoclinic zirconia solid solutions were stabilized in the presence of Ca ions. When 20 and 30 wt% of CaO were added, cubic zirconia and CaZrO3 solid solutions were observed above 700°C. At the CaO rich-end, the coexistence of calcium carbonate polymorphs as vaterite and calcite were observed. Anhydrite was present across the entire range of compositions studied from 300 to 900°C.

Catalysts based in titania mixed with tungstophosphoric acid (TPA), H3PW12O40, in various proportions (1, 15, 25 and 50 wt%) were obtained by the sol–gel method. The gels were prepared by hydrolysis and gellation of titanium n-butoxide with a TPA solution, using HNO3 as a catalyst to obtain a pH 3. Fresh samples were thermally treated from 100 to 800 °C, in a stepwise increment of 100 °C during 20 h per step. Specific surface areas were calculated by the BET method from the nitrogen adsorption isotherms; it was found that the surface area increased with TPA content. The crystallization behavior was followed by powder X-ray diffraction. Crystallite size measurements showed that anatase remains nanocrystalline in the studied temperature range. From the X-ray data, it was clear that below 700 °C TPA is highly dispersed in an amorphous state.

Sulfated and phosphated titania (TiO 2 ) were obtained by the sol–gel method. The sulfation was prepared in situ using sulfuric acid as hydrolysis catalyst, or by impregnation with ammonium sulphate. Phosphated sol–gel titania was synthesized with phosphoric acid. Long thermal treatments were carried out from 100 to 1000 °C to study the crystallization process of titania. All present phases were nanocrystalline, and the anatase–rutile polymorphic transformation was dependent on the crystallite size of the materials and on the preparation method. The smallest crystallite values were obtained for the phosphated samples. Titania sulfated by impregnation was found to be an efficient and selective catalyst towards propene, whereas di-isopropylether was obtained only in the catalyst prepared in situ with H 2 SO 4 .

Aluminum thin films deposited by free evaporation on silicon substrates were studied by X-ray diffraction and Auger electron spectroscopy. The crystalline behavior was analyzed by X-ray grazing incidence, when DC current cycles (0.1–1.2 A) along the metallic films were applied in situ. The intensity, Full Width Height Medium (FWHM), and the crystal parameter changes as current is applied, due to the film relaxation and thermal expansion. It was found that Al thin films behave as an elastic system when the electrical current is cycling. Stresses due to the differential thermal dilatation of film are analyzed as a function of the current flow (Joule effect). Also, the aluminum oxide layer, formed on the surface of the metallic film, plays an important role on the oscillating process found on aluminum films due to the number of applied current cycles. D 2004 Elsevier B.V. All rights reserved.

Copper-doped zirconia (1% mol) and zirconia powders were prepared by the sol–gel process, using zirconium n-butoxide and copper nitrate as precursors. The resulting xerogels are nanocrystalline and exhibit different properties from the corresponding microcrystalline materials. The copper nitrate salt was dissolved and co-gelled in situ at the initial stage of the reaction. The properties of the resulting materials were studied by XRD, FTIR and UV-Vis. The as-prepared samples were amorphous and crystallized to the tetragonal zirconia phase at 400 °C. At temperatures higher than 600 °C, the monoclinic phase was also obtained. No evidence of discrete crystalline copper compounds was observed, consistent with good dispersion of the dopant. Several bands were observed by FTIR in the 4400–3000 cm−1 region, which diminishes in intensity and shifted to higher wavenumbers with heating. The bandgap energy (E g ) was strongly modulated by the presence of the dopant and heating temperature, with increasing temperature leading to a corresponding decrease in E g .

Mixtures of ZrO2-CaSO4 in different molar ratio were prepared by the sol–gel method. The precursors were anhydrous calcium sulfate (CaSO4) and zirconium n-butoxide in ethanol. Sulfuric acid was used as a hydrolysis catalyst to carry out the reaction at pH 3. The samples were thermally annealed and characterized by X-ray powder diffraction (XRD). Crystalline structure for selected samples (100, 90, 80% molar ZrO2), were refined by the Rietveld method. Tetragonal zirconia and anhydrite were obtained in all compositions ranges, from 400 up to 800°C, although baddeyelite appears in the zirconia rich end (98% molar) from 600°C. Towards high calcium content, different nanostructured calcium sulfates as gypsum, bassanite and anhydrite were obtained.

An alternative method to diminish the nitrogen pollutant levels in waste waters is to encapsulate microorganisms whitin ceramic materials. The sol–gel method has been extensively used for the preparation of such kind of materials permitting a higher stability and viability of useful organisms. In this work, the thermal characterization during dehydration of nitrifying and denitrifying aqueous emulsions of mud encapsulated in sol–gel silica is presented during the process of dehydration in ambient conditions and as a function of temperature. The characterization was performed by a photopyroelectric (PPE) technique, whose detector was made with a 110 mm polyvinyldifluoride (PVDF). The cell was constructed in such a way that the sample was inside the cell, and the bottom of the cell was closed by the PVDF foil. Thermal effusivity as a function of temperature was obtained illuminating the PVDF directly by a modulated 1W tungsten lamp. The sample is enclosed inside a chamber, using a Peltier cell that controls temperature in a range from 40 to 27 ◦ C. The sample is on top of the PVDF, which is illuminated by the modulated tungsten lamp.

Thermal effusivity evolution as a function of time, of aqueous emulsions of agar encapsulated in a TiO2 matrix synthesized by the sol–gel method, was monitored during dehydration at ambient conditions. Measurements of thermal effusivity were performed by the photoacoustic technique using a conventional cell. The results show sigmoidal growth as a function of time during the dehydration process. The data analysis shows two dehydration stages; in the first one, samples prepared at pH 7.5 show a lower dehydration time than samples prepared at pH 7. But, when the dehydration process continues, it is slowed down in the sample prepared at pH 7.5. FT-IR absorption and Raman spectroscopy are used to verify the strong interaction between the TiO2 matrix and the agar.

Polycrystalline cadmium sulfide (CdS) thin films were deposited on glass substrates by chemical bath deposition (CBD) and close-spaced sublimation (CSS) techniques. The typical deposition temperatures between these techniques are quite different. The CdS thin films deposited by CBD were prepared using two methods of bath agitation: magnetic and ultrasonic agitation. We found that films deposited with ultrasonic agitation presented a cleaner surface with minor presence of contaminants, similar to the obtained for CSS films, as demonstrated by Auger analysis. Properties of the CdS films such as morphology, optical transmission, crystallinity and band gap energy, are discussed in order to compare them in both techniques. We obtain that crystallinity of CdS films depends strongly on the temperature used for deposition. In agreement with several works, films prepared by CBD technique presented a cubic structure, while films grown by CSS technique exhibited an hexagonal symmetry.

The subsolidus phase diagram, CaO–Al2O3–CoO, and its phase relations below 1300°C have been studied in air. The stability regions of nine subsolidus compatibility triangles were established and a new ternary phase was found. The structure of this compound, Ca3CoAl4O10 (orthorhombic, space group Pbc21, a=5.1452(2) A, b=16.7731(5) A, c=10.7055(3) A), was determined from X-ray diffraction data and found to be isostructural with Ca3ZnAl4O10. This is an open framework compound with three crystallographically different channels, each with a diameter of ∼3.5 A. The two end members of the binary CoO–CaO system are surrounded by small regions of solid solutions. Lab color parameters were measured in several compositions. No ternary phases were found when Co was substituted by other divalent cations such as Sr, Ba, Mn, Ni, Cu, Cd, Sn and Pb.

Zn7/3Sb2/3O4 is a secondary phase in ZnO-based varistors. Acceptor impurities, such as Li+, increase the resistivity. This effect is produced by a modification of the grain boundary barriers. The role of the cationic distribution in the mentioned events is worth clarifying. The Li0.5Zn5/3Sb2.5/3O4 room-temperature structure was determined by means of a neutron diffraction and synchrotron X-ray diffraction investigation. The title compound was prepared by conventional ceramic process. The elemental composition of the investigated sample was verified by means of electron microscopy—energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The neutron experiment was performed at the high-intensity neutron diffractometer with position-sensitive detector at the D1B beamline of the Laue-Langevin Institute, Grenoble. The high resolution synchrotron measurement was carried out at MCX beamline of Elettra Sincrotrone Trieste. Rietveld analysis was performed with the FullProf program. Li0.5Zn5/3Sb2.5/3O4 belongs to the spinel family, space group F d 3 ¯ m (227). The measured lattice parameter is a = 8.5567(1) Å. The Li+1 and Zn+2 ions are randomly distributed among the tetrahedral and octahedral sites as opposed to Sb+5 ions which have preference for octahedral sites. Fractional coordinate of oxygen, u = 0.2596(1), indicates a slight deformation of the tetrahedral and octahedral sites. The data given in this paper provide structural support for further studies on measurements and microscopic explanations of the interesting properties of this family of compounds.

We studied the formation of the band gap on CdS thin films deposited on glass substrates by chemical bath deposition (CBD) and close spaced sublimation (CSS) techniques. In order to obtain the first stages of films growth, we used small deposition times for both methods. Films growth by CBD were prepared by two modalities on the bath agitation: magnetic agitation with a magnetic stirrer, and a new proposal based on ultrasonic vibration. Morphological, structural, and optical results were obtained on films. Values of the band gap energy obtained by the absorption method, are agree with the values reported in the literature, but squared absorption coefficient vs. energy curves, showed differences between them. An explanation on this behavior with the optical window effects, the surface roughness, the structural results, the films thickness, and the growth technique is given. CBD technique with ultrasonic vibration produces films with more cleaner surfaces and better optical properties.

The influence of a chromate film on the corrosion behaviour of Zn, Zn–Co and ZnFe coatings was investigated. XPS, AES techniques were applied for characterisation of the iridescent chromate films, while the XRD method was used for the corrosion product analysis. Atmospheric field (4 years data), accelerated (neutral salt spray and SO2 cabinet) tests and electrochemical measurements were applied for the corrosion resistance studies. The beneficial influence of alloying for chromated Zn electrodeposits was observed under the conditions, where Cl− ions were the dominant pollutant (marine test site, Cl− cabinet, Cl− aqueous solution). The degree of protection from the chromate film, in spite of their lower thickness, was detected to be higher for the alloyed samples. A higher concentration of Cr(VI) compounds in the passive chromate layers of alloyed samples may be the reason of their superior corrosion resistance.

ZrO2–SiO2 sol–gel powders were produced using tetraethoxysilane (TEOS) and zirconium propoxide. After gellation, the ZrO2 crystallization process was investigated using X-ray diffraction (XRD), thermal analysis (DTA/TGA), and scanning electron microscopy (SEM). Fresh gels were amorphous. Thermal treatments were carried out from 100 to 1400°C for a total annealing time of 182 h. Tetragonal zirconia, (Z(t)) was the first phase to crystallize, between 300 and 500°C. Crystallization temperature was lower for zirconia-rich compositions, increasing as silica content was raised. DTA analysis showed that Z(t) crystallization occurred in two stages. Complete tetragonal–monoclinic zirconia transformation occurred near 1000°C, and was clearly observed only in ZrO2-rich compositions (>80%). Silica remains amorphous until 1200°C, when ZrSiO4 formation took place. A metastable sol-gel phase diagram was proposed to show the crystallization process between 100 and 1400°C.

The subsolidus phase diagram CaO-Al{sub 2}O{sub 3}-Ta{sub 2}O{sub 5} has been determined at 1300--1350 C. Two ternary phases are present, Ca{sub 2}AlTaO{sub 6} and the new phase, CaAlTaO{sub 5}. From Rietveld refinement of powder X-ray diffraction data, CaAlTaO{sub 5} has the sphene structure, monoclinic 6.6760(3), 8.9546(3), 7.3494(3) {angstrom}, {beta} = 114.098 (3){degree}, space group C2/c, and Ca{sub 2}AlTaO{sub 6} has a partially ordered double perovskite structure, monoclinic 5.3915(3), 5.4321(4), 7.6508(4) {angstrom}, {beta} = 90.076(5){degree}, space group P2{sub 1}/c. The Al and Ta cations form a rock-salt-type arrangement with 3% cross substitution of Al on Ta sites and vice versa.

The photoactivation time of sol–gel nanostructured titania, in an ethanol suspension, was studied by optical methods in the UV–Vis region. Titania activation was induced using a Hg lamp and the process was analyzed using light transmittance. The Hg lamp light beam was transmitted through the sample and collected with a spectrophotometer as a function of time. The titania powder was thermally treated to observe the effect in the photoactivation. When the photoactivation of the titania suspension occurs, the transmittance falls and afterwards, a constant value is reached. It was found that the activation time depends on the crystalline structure and the crystallite size.

Sol–gel silica reservoirs were synthesized using tetraethoxysilane and functionalized with OH groups to stabilize dopamine into a ceramic matrix. The synthesis was made in air and N2 atmosphere. The dopamine–silica reservoirs were analyzed by FTIR spectroscopy, DTA–TGA and BET techniques. Nanostructured materials with a high specific surface area (500 m 2 /g) and a mean pore size between

We studied changes induced by electrical current (DC) on gold thin films by using a combination of scanning tunnelling microscopy and grazing incidence X-ray diffraction. The results show that the process inducing device failure is based on surface diffusion that produces the growth of microcrystals at the expense of mechanically strained microcrystals. The de-percolation and loss of adherence to the substrate reduce the heat transfer which in turn produce an increase of film temperature. This temperature increase induces a large mechanical stress due to the differential dilatation of substrate and film. The result of these processes is the final failure of current conduction by the film.

We study the modification of gold thin film surface by Scanning Tunnelling Microscopy (STM) and grazing incidence X-ray to understand the process of electromigration. As a result of the applied current we have observed by STM a large movement of matter in the film surface that results in a strong rearrangement and modification of all the surface structures in a matter of minutes. We obtained that the 〈111〉 peak position shift towards the gold standards with elapsed time indicating that the surface strains formed during film growth disappears. The conclusion of the study is that the electrical current induces a rearrangement of the gold film surface.