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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.

Industrial and vehicular emissions of particles cause multiple damages to human health due to concentration, size, and composition. These emissions contain magnetic particles; therefore, low-cost properties allow tracking and monitoring them. This study is aimed at identifying the primary sources of magnetic material in 100 samples of urban road dust from San Luis Potosi, Mexico, analyzing the influence of land use and the type of road on these particles. Magnetic susceptibility (χlf) and isothermal remanent magnetization at 0.7 T (IRM0.7T) were determined, as well as the iron and manganese content using X-ray fluorescence. The distribution of particles was examined by land use and type of road through geostatistical maps and variance analysis. The results showed that the iron and manganese content, χlf, and IRM0.7T were positively correlated, indicating a possible common origin. The primary sources identified were the iron smelter and laminator in the industrial park. Urban land use influenced the content of iron, manganese, and magnetic material in urban road dust. The land uses with the more significant transformation (industrial and mixed) presented the highest values of iron, manganese, χlf, and IRM0.7T. On the other hand, vehicular traffic was indirectly assessed through the type of road, influencing the magnetic signal of urban road dust and finding the highest signals in primary and secondary roads. Then, the magnetic properties allowed the tracking and monitoring of magnetic particles from industrial and vehicle emissions.

Zn is an essential trace metal in living beings. However, excessive concentrations can cause toxic effects even in the aquatic biota. Zn is widely used in different industrial sectors, which has increased its presence in aquatic environments. To assess the acute toxicity of Zn, bioassays were performed with the fish Gambusia sexradiata for a 96-h exposure using ZnCl2 (0 and 15 salinity) and ZnO nanomaterials (0 salinity). The mean lethal concentrations (LC50–96 h) for ZnCl2 were 25.36 (19.64–32.76) and 177.91 (129.39–244.63) mg Zn L−1 to 0 and 15 salinity, respectively. The increased concentration of ZnCl2 showed a dose-response relationship; similarly, the increase in salinity significantly reduces the toxicity of Zn. Characterisation of ZnO nanomaterials was carried out by FTIR, DRX, SEM, DLS and zeta potential. The FTIR spectra showed the characteristic band of Zn-O vibration at 364 cm−1, while DRX presents the hexagonal wurtzite structure with an average crystallite size of 40 nm. SEM micrographs reveal rod-like shapes with lengths and diameters of 40–350 nm and 90 nm, respectively. Agglomerates of 423 nm in water suspension were obtained by DLS and zeta potential of + 14.4 mV. Under these conditions, no mortality was observed due to the rapid flocculation/precipitation of ZnO nanomaterials, which involved brief interaction periods of Zn in the water column with the fish. Gambusia sexradiata is affected by increased Zn concentrations in hard water conditions, and salinity changes modified Zn toxicity, placing it as a suitable model for toxicity tests for this type of particles.

The ethanol dehydration and subsequent ethylene oligomerization to short-chain olefins using catalysts based on ZSM-5 zeolite was studied in detail. P, Fe, and Ni were added by incipient wetness impregnation on zeolites with two SiO2/Al2O3 molar ratios (50 and 80). The catalysts were characterized by N2 adsorption–desorption, XRD, SEM–EDX, FTIR spectroscopy of adsorbed pyridine, and XPS techniques, while the catalytic activity was evaluated using an isothermal fixed-bed reactor. The impregnation of P, Fe, and Ni significantly improved the formation of the desired C3+ olefins (olefins having three or more C atoms). Particularly, the zeolite with SiO2/Al2O3 molar ratio = 50 and impregnated with P, exhibited the highest selectivity (C3+ olefins > 45 wt% at TOS = 5 h) in comparison with the rest of the evaluated catalysts. On the contrary, catalysts with SiO2/Al2O3 molar ratio = 80 showed lower selectivity to C3+ olefins, producing more side products (i.e. paraffins, aromatics and diethyl-ether).

This study presents the synthesis and physicochemical characterization of functionalized carbon-based materials prepared from cassava residues (Manihot esculenta). Cassava residues were obtained from a local market, washed, dried and ground to small particle size. This powder was mixed with different aqueous media: diluted sulfuric acid (0.2 M), nejayote and deionized water. These mixtures were treated in an autoclave at 200 °C for 4 h. The physicochemical characteristics of samples were studied by SEM, TGA, FTIR, XPS and elemental analysis. The chemical composition of C:O was similar among groups, but TGA suggested that the hydrochar prepared with sulphuric acid presented a better thermal stability, with a decomposition peak at 435 °C, which was 80 °C higher than samples prepared with deionized water. The acid sample also had lower mass loss (47.3%). The SEM images showed that sulphuric acid promoted the formation of small needle-like structures, while samples prepared using nejayote and water showed agglomerates with a few spherical shapes. The proximate analysis indicated that there was a carbon enrichment from 41% from the original sample to 62% after the hydrothermal process.

This study was undertaken to evaluate the adsorption of Reactive Black 5 dye (RB5), in aqueous solution, onto MCM-41 mesoporous silica nanoparticles (MSNs) functionalized with 3-aminopropyltriethoxysilane (APTES) by two methods: co-condensation and post-synthesis. The morphological and surface properties of both functionalized materials were compared by SEM, SAXS, N2 sorption and XPS characterization techniques. Sorption experiments were performed in order to determine the effect of pH, contact period and initial concentration of aqueous RB5 on the adsorption properties of bare- and both types of amino-MSNs. The results show that there exist morphological changes in the nanoparticles according to the type of functionalization synthesis, i.e. loss of hexagonal structure in co-condensation method and more density of amino groups on the surface of post-synthesis functionalized materials. The adsorption of RB5 on both type of materials is independent of the pH since they present adsorptions close to 100% in the evaluated pH range. The best fit of the data from adsorption kinetic studies is a pseudo-second-order model, being the material functionalized by the co-condensation method, which presents a higher adsorption rate because of its greater pore volume. The adsorption isotherms fitted well to the Langmuir model, with the amino-MSNs functionalized via the post-synthesis method presenting a higher capacity of adsorption, due to a greater density of amino groups on its surface, thereby facilitating their interaction with the RB5 molecules. Altogether, the results indicate that the type of functionalization synthesis affects the morphological characteristics of the nanoparticles and these, in turn, modify their adsorption properties.

The establishment of microorganisms and particularly fungi on rock surfaces, which is favored by humid tropical climates, may accelerate the degradation of historical monuments and buildings and thereby cause the irreversible loss of rich cultural heritage. Therefore, it is urgent to search for new ways to preserve such buildings. The in vitro antifungal activity of calcium zinc hydroxide dihydrate [CaZn2(OH)6·2H2O] (CZ) synthesized via the sol–gel method has been previously reported for limestone. The present study reports for the first time, the minimum fungicidal concentration (MFC) of CZ obtained via mechanochemical processing, against diverse fungi involved in biodeterioration processes of limestone and dolostone. We found that CZ nanoparticles had a fungicidal effect on all evaluated fungi, at concentrations of 156–1250 μg/mL. The MFC depends on the number of cells in conidia and the presence of melanin in cell walls. For these reasons, Pestalotiopsis maculans and Curvularia lunata, which had more than four cells and melanin pigmentation, both required a greater CZ concentration (1250 μg/mL) for inhibition, compared with species from the genera Penicillium oxalicum and Aspergillus niger, which had one cell and were strongly inhibited. Thus, CZ nanoparticles are promising candidates for application in treatments to restore the cultural heritage.

This report describes the synthesis of a controlled drug delivery system that was obtained by coating mesoporous silica nanoparticles (MSNs) with poly(β-amino ester) (PbAE), which is a solid and stable material at physiological pH, but is dissolved at acidic pH values, such as those in tumor tissues (from 5.0 to 6.5). To synthesize the system, PbAE chains were grafted onto amino-functionalized MSNs through a reaction between the surface amino groups of MSNs and the ends of acrylate chains of a PbAE. The system was physicochemically characterized by dynamic light scattering (DLS), Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, X-ray photoelectron spectrometry, and X-ray diffraction analyses. In addition, the in vitro release of doxorubicin (DOX) and doxycycline (DXY) in acidic and physiological media was evaluated. It was observed that the PbAE modification did not affect the mesoporous structure of MSNs. When the amount of 3-aminopropyltriethoxysilane was increased during functionalization, the amount of PbAE binding to MSNs increased as well. With respect to drug release, the sample with the highest amount of PbAE showed better control in the delivery of DXY and DOX in acidic media, because at pH 5.5, the release of both drugs was 40% higher than that at pH 7.4. These results reveal two aspects about the presence of PbAE in MSNs: PbAE does not affect the mesoporous structure of the nanoparticles, and PbAE is the main factor controlling the delivery of drugs in acidic media.

{Pt, Ir}/Ce1-xRuxO2, catalysts were prepared to be used in the hydrogen production from the ethanol steam reforming reaction. Initially, the catalytic supports, Ce1-xRuxO2, were synthesized by the sol–gel process. Later, the Pt/Ce0.97Ru0.03O2 and Ir/Ce0.97Ru0.03O2 catalysts were produced through incipient wetness impregnation using high purity compounds as sources of Pt or Ir. These systems were characterized by means of SEM, XRD, TEM, and specific surface area measurements. The catalysts were tested in the ethanol steam reforming reaction at stoichiometric conditions (water/ethanol = 3) in a continuous flow fixed–bed quartz microreactor under atmospheric pressure in the temperature range of 300–600 °C. From the results, it follows that the support itself acts as a catalyst for the reaction. The catalytic support (Ce0.97Ru0.03O2) and the catalytic species (Pt, Ir) exhibit sustained conversion during the studied interval of temperature. It was observed that at 600 °C, Pt/Ce0.97Ru0.03O2 and Ir/Ce0.97Ru0.03O2 achieve a (5 H2/ethanol) molar ratio. Stability tests revealed that Pt/Ce0.97Ru0.03O2 and Ce0.97Ru0.03O2 compounds showed an outstanding performance in the ethanol steam reforming reaction for more than 10 h before being deactivated.

Different aspect ratio nanostructures of pure ZnO and Zn(1−x)EuxO were produced through the application of a statistical factorial design 23. The procedure consisted of two stages. First, the growth of ZnO thin films by atomic layer deposition on silicon (111) substrates, by decomposition of the metal precursor, diethyl zinc, at 190 °C and 0.25 Torr. In the next stage, those films were processed using the microwave-assisted hydrothermal method to promote the growing of ZnO nanostructured compounds, using a precursor solution of Zn(NO3)2·6H2O and hexamethylene tetramine, acting as a bi-dentate ligand capable of bridging two Zn2+ ions in solution. In addition, europium-doped ZnO (Zn(1−x)EuxO) and ZnO nanostructures were produced using Zn(NO3)2·6H2O and Eu(NO3)3·5H2O. The experimental levels (values) considered for every factor were Eu3+ concentration (0.02 and 0.06, atomic, %), temperature (80° and 120 °C) and time (30 and 50 min). The synthesis products were characterized through X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and photoluminescence measurements. Our results demonstrate that it is possible to produce nanostructures with specific size, morphology and physical properties depending on the specific synthesis based on our proposed experimental design.

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.

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.

Microwave hydrothermal synthesis, using an experimental 23 factorial design, was used to produce tunable ZnO nano- and microstructures, and their potential as photocatalysts was explored. Photocatalytic reactions were conducted in a microreactor batch system under UV and visible light irradiation, while monitoring methylene blue degradation, as a model system. The variables considered in the microwave reactor to produce ZnO nano- or microstructures, were time, NaOH concentration and synthesis temperature. It was found that, specific surface area and volume/surface area ratio were affected as a consequence of the synthesis conditions. In the second stage, the samples were plasma treated in a nitrogen atmosphere, with the purpose of introducing nitrogen into the ZnO crystalline structure. The central idea is to induce changes in the material structure as well as in its optical absorption, to make the plasma-treated material useful as photocatalyst in the visible region of the electromagnetic spectrum. Pristine ZnO and nitrogen-doped ZnO compounds were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (BET), XPS, and UV–Vis diffuse reflectance spectroscopy. The results show that the methodology presented in this work is effective in tailoring the specific surface area of the ZnO compounds and incorporation of nitrogen into their structure, factors which in turn, affect its photocatalytic behavior.

Rocks are composed of minerals, bounding matrix, cracks and pores. The study of changes in the physical properties of rocks as a function of heat treatment is relevant to various engineering and industrial applications. The effect of thermal damage on the compression, strength, ultimate compression strain, color and loss of mass of two different limestones extracted from the Yucatan Peninsula is studied. Different thermal treatments are applied by heating the sample from room temperature up to 600°C, with steps of 100°C. The results show a high correlation between the heat transport characteristics, mechanical properties, content of organic matter and the presence of carbonates and iron oxides in each type of limestone rock.

This contribution shows the results of a study carried out in order to determinate the deterioration mechanisms suffered by stucco masks from the important archaeological Mayan site of Edzná, Campeche, México; due to their long exposition to the tropical environment of the zone. Stratigraphic analysis of fragments from the masks containing pigments and surface neoformation products, were analyzed by optical microscopy and scanning electron microscopy coupled to a secondary X-ray emission system. Crystalized salts mineral composition were characterized by X-ray diffraction. Also, during the study, environmental parameter like temperature and relative humidity were monitored in site. Results indicate that stuccos mineral matrix is formed by calcareous materials, covered by films with variable proportions of ferrous materials (red, ochre and yellow colors) and rich carbon content (black color). Compounds were associated to blue and green colors. Al these materials showed a high level of deterioration because of differential forces caused by stucco and deposits of environmental soluble salts during dissolution crystallization cycles caused by humidity differences between stucco and environmental as a consequence of their particular exposure conditions.

Moisture is a critical control of chemical and physical processes leading to stone deterioration. These processes can be enhanced by microbial biofilms and associated exopolymers (EPS). There is limited current understanding of the water transport process across rocks covered by EPS. In the present work, we employed the photoacoustic technique to study the influence of three biopolymers (xanthan, microbactan and arabic gum) in the water transport process of two types of limestone rock of similar mineralogy but contrasting porosity. Both controls of RL (low porosity) and RP (high porosity) presented the higher values of water diffusion coefficient (D) than biopolymer-coated samples, indicating that biopolymer layers slowed down the transport of water. This trend was steeper for RP samples as water was transported seven times faster than in the more porous rock. Important differences of D values were observed among samples coated by different biopolymers. Scanning electron microscopy and optical microscopy showed that surface topography was different between both types of rocks; adherence of coatings was seen predominantly in the less porous rocks samples. FTIR and NMR analysis showed the presence of pyruvate and acetate in microbactan and xanthan gum, suggesting their participation on adherence to the calcareous surfaces, sealing surface pores. These results indicate that water transport at rock interfaces is dependent on the chemistry of biopolymer and surface porosity. The implications for reduced water transport in stone conservation under the influence of biopolymers include both enhanced and lower deterioration rates along with altered efficiency of biocide treatment of epilithic biofilms.

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.

This dietary study compares concentrations of trace elements in human skeletal series from the municipal cemetery of Xoclán, in Mérida, Yucatan, and a skeletal collection that was donated by the Yucatecan State Justice Department (PGH). The results from these modern samples are to be compared to those obtained from human collections from a colonial cemetery from Campeche and the pre-Hispanic Maya site of Xcambó. Our results indicate that the archaeological series show higher concentrations of Sr compared to the modern populations, both of which showed very similar values. Zn concentrations were similar when the modern values were compared to those derived from the colonial series from Campeche. Xcambó´s population, in turn, shows a high degree of variability in Zn values, which may be due to diagenetic contamination.

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.

Black corals (Antipatharians) are colonial cnidarians whose branched tree-like skeleton is constituted of chitin fibrils inside a lipoproteic matrix. The arrangement of the constituents of these materials provides a structure with outstanding physical properties. In this study, the structural properties of black coral skeletons of Antipathes caribbeana and Antipathes pennacea species are explored by means of thermal treatments in the range from room temperature up to 400 °C and the subsequent analysis using X-ray diffraction (XRD), infrared spectroscopy (FTIR), and thermal analysis (DSC/TGA). The effects of thermal treatment from room temperature up to around 210 °C induce the enhancement of the bands in the FTIR spectra and X-ray diffractograms, above that temperature, the FTIR and X-ray peaks become strongly attenuated. These effects are specially observed in the infrared bands associated to chitin at 3298 cm−1 and to the secondary amide stretching around 1663 cm−1, in particular, allowing the identification of the α-chitin in the black coral. XRD shows that the crystallinity index of the black coral chitin at room temperature is 24% and grows when the temperature increases, reaching a maximum value of 37% at 210 °C and decreases for higher temperatures. In addition, DSC and TGA measurements allowed identifying the most important transformation stages during the thermal treatments, namely, evaporation of water and the beginning and progress of degradation, depolymerization, and denaturation processes and finally, the degradation of the main functional groups of coral skeleton and coral chitin, in which the polysaccharide structure of chitin is depolymerized and the protein matrix is denatured.

Titania Degussa P25 powder was treated with Argon (Ar) and Nitrogen (N2) gas plasma inside of a closed homemade chamber system at 50 Pa of pressure. The electric discharge was generated applying an AC voltage (0–15,000 V) to a pair of aluminum electrodes. Two sets of samples were analyzed. In the first one, the plasma is applied directly on a layer of titania P25 that is spread out on top of one of the electrodes and, in the second one, a gold foil substrate is positioned between the titania powder and the electrode, named TiO2/Au. In the last sample, gold coated titania nanoparticles or clusters of gold are formed, changing the optical properties of the material. The evolution of the optical properties of the obtained samples was analized using UV–Vis diffuse reflectance. The spectra show a shift in the band gap and a broad band in P25/Au associated with the gold plasmonic band. Additionally, the photocatalytic activity was evaluated by monitoring the photodegradation of methylene blue solution (0.01 g/L), using UV–Vis absorption analysis in the range 250–850 nm. After the plasma is applied, the gold impregnation over the titania surface increases the photocatalytic activity.

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.

Climatic changes and the increased air pollution intensify the atmospheric degradation of stone, affecting the aspect and integrity of valuable historical buildings constructed using limestone and located in tropical coastal sites. This paper analyzes limestone degradation process due to air pollution and humidity in tropical humid conditions in historical buildings located in the cities of Havana, Cuba and San Francisco de Campeche, Mexico. Havana shows higher pollution level than San Francisco de Campeche, which presents pollution levels as a consequence of a multipollutant situation along with the presence of airborne salinity. Temperature and humidity data were recorded from the walls of historical buildings in the city of Havana: the Minor Basilica and the convent of San Francisco. Changes in dry/wet cycles due to the absence of direct sun radiation as well as a high level of SO2 allow the formation of a black crust (mainly composed of gypsum) in the lower part of the surface of the facade of the Basilica Minor in Havana; however, crusts formed in historical buildings located in San Francisco de Campeche City are mainly composed of calcium carbonate, indicating the importance of natural degradation mechanisms mainly due to dissolution in water. In the last case, the influence of water plays an important role in the development of biodegradation, which induces the formation of calcium oxalates. Caves and cracks were found in the walls of military buildings caused by water infiltration. The influence of air contamination, humidity, and construction materials determine the type of degradation that historical buildings undergo.

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.

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.

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.

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.

We used the photoacoustic technique for characterization of the thermal properties of adult shells of American oyster Crassostrea virginica (Gmelin, 1791) and the mussel Ischadium recurvum (Rafinesque, 1820). Heat transport is more efficient in C. virginica than in I. recurvum shells, reflecting the different architecture, microstructure, and composition of the two kinds of shells.

Knowledge of the mechanical and petrographic properties of limestone rocks is an important issue to different areas of science and engineering. Sedimentary limestone rock is one of the most abundant materials in the Peninsula of Yucatán used for decorative and building construction. This work studies the petrographic, mineralogical, and physical properties of three different types of limestone slabs of the state of Yucatán.

Fourier Transform infrared spectroscopy has been employed to study the shells of two kind of mollusks, American oysters (Crassostrea virginica) and mussels (Ischadium recurvum). It is shown that it is possible to distinguish the different calcium carbonate lattice vibrations in each case, mussel shells present aragonite vibration frequencies, and the oyster shells present those corresponding to calcite. The superposition, shift and broadening of the infrared bands are discussed. Changes in the vibration modes due to successive thermal treatments are also reported.

Most of the inorgaiiic hiomineralized matcrials are deposited on an orpanic matrix that controls thc orientation and structure of the crystals. It is thought that chcmical groups at tlic suriace oi thc matrix may act as a tcmplaie for the nucleation and growth of the mineral. A x-ray diiiraction study of the texturization development of the bivalve mollusk sh~lls is preseiiteu: spccifically. !he mussel Ischurlirrnr r-rcrrnwu (Rafinesque. 1870). in different growing stagcs. Tlic x-ray reflections show a preferred orieiitation thnt changes as thc mollusk gows, and at tlic final stages oiily two crystallographic plancs prcvail. In the last deciides a great effort has heen dedicated to study and to understaiid naturiil hiomineralized niaterials. in order to desigii nnd develop new advanced materials with spccific properties to use thcm on different tcchnology applications [1.2]. For iiistaiice, the production oF cenients with a hiph hardness and free oi mncro-defects. can be improved by imitating the high resistance and hardncss of the nacre produccd by a species of marinc hivalve (mother of pciirl) 131. There has heen a great interest to study thc growth mechanisms of the crystals developcd hy liviiig organisms. as well as the variatioii oF their propenies with the agiiig of the orgaiiism. iiiiu to undcrstand their difierences with the geologic;il world. In Geology. the stable crystal phiiscs are iormed under cenain conditions oF ieiiiperature. pressure. etc. Meanwhile in the hiology world the organisins maintaiii a strong coiitrol durine growth which also is influenccd by ihc environmental coiiditions that could rcsult in the dcvelopmcnt of prefcrrcd orieiitation of tlic crystals. Crystals in living systems grow up iii a controlled shape under the dircctioii of thc orgmic molecules and tissues. ln the niiiierals the crystals generally are precipitated Froni solution or from solidification oF a meltcd material: in contrast. thc inorganic materials in liviiig orgaiiisms grow froin the organic matrix u.hich has a strong influeiicc to define the crystal .;li;ipc aiid the crystalline ph;ise io be developcd. For exiimple the shells of ihe mollusks start to grow From their edges where two polyniorphs oF calcium carbonate. calcite and ar;igonite. are foniieu within a protein niatrix. In this work ihe study of the teXturimtioii of the crystallinc phascs during succcssivc stagcs of growth iii tlie iiiussel Is