Search

Nanocomposites of polyvinyl acetate and silica are prepared by sol-gel method. Samples are characterized using Infrared Spectroscopy, Thermal Analysis (TGA-DTGA) and X-ray photoelectron spectroscopy. In the hybrids with higher content of silica, it is evidenced the presence of hydrogen bonding between the residual silanols on the silicate network and the carbonyl of PVAc, this is determined by FTIR and XPS. It was also found that the hybrid containing 75% of silica suspension and 25% of polyvinyl acetate was the most thermally stable by TGA-DTGA.

A new nanocomposite material involving multi-walled carbon nanotubes (MWCNTs) was synthesized using the traditional chemical vapor deposition (CVD) method. The objective of this investigation was to embed and encapsulate metal (cobalt) nanoparticles inside the MWCNTs in a one-step CVD process. The morphological and structural characterization of MWCNTs-based nanocomposites was performed using scanning electron micrscopy (SEM), high resolution transmission electron microscopy (HRTEM), thermal gravimetry analysis (TGA), Brunauer, Emmett and Teller theroy (BET surface area), and Raman spectroscopy. HRTEM confirmed the formation of Co encapsulated MWCNTs (Co@MWCNTs), whose average diameter was 27 nm. Surface area of the nanocomposites was determined by the BET method, which was found to be 40 m2 g−1 for the MWCNTs and 120 m2 g−1 for the Co@MWCNTs nanocomposite, respectively. The crystallinity of the MWCNTs and Co@MWCNTs was analyzed using Raman spectra, where the ratio of intensities of D and G band for the MWCNTs was 0.94 and 0.80 for the Co@MWCNTs, respectively. Electrochemical evaluation of the Co@MWCNTs nanocomposite was performed by cyclic voltammetry in 5 M KOH solution. The Co@MWCNTs nanocomposite displayed oxidation in alkaline media with onset potential at 0.55 V vs. SHE. This new approach of synthesizing nanocomposites where metal particles are encapsulated between the walls of MWCNTs could lead to the development of new, efficient and interesting electrocatalysts.

Simple equation Mt/M∞ = Ktn is evaluated to describe the Fickian mechanism of oil absorption and water release during the frying of tortilla chips in nixtamalized samples with lime and without lime where Mt/M∞ is the fractional solute absorption or release, and n is the diffusional exponent characteristic of the Fickian mechanism that changes with food physical and chemical properties. For the Fickian mechanism, the exponent (n) is ≤0.50, and non-Fickian is 0.5

In this work, an enzyme extract immobilization over carbon nanomaterials is presented; that is, carbon nanospheres (CNSs), and multi-walled carbon nanotubes (CNTs), using covalent bonds with glutaraldehyde as a crosslinking compound. Carbon nanostructures were obtained by chemical vapor deposition using an iron–cobalt powder alloy prepared by the sol–gel process and using silica powder as support. Acetylene gas was used as carbon carrier to prepare both the CNTs and CNSs. Both nanostructures were oxidized with an acid treatment in order to add functional groups to the surface and subsequently immobilize the enzymes. Carbon nanostructures were characterized using scanning electron microscopy, infrared spectroscopy and Raman spectroscopy to confirm oxidation, immobilization and structural properties. Electrochemical impedance spectroscopy revealed that carbon nanostructures improve the electron transfer of the electrode. Finally, the cyclic voltammetry provided information about the redox process before and after immobilization. Even more, the catalytic activity of the enzymes extract was evaluated showing that CNSs are the best support.

For many years, in electrochemical processes, carbon nanostructures with metal support have been employed as electrodes due to their high surface area, chemical stability, and excellent performance as catalyst support by allowing a better electronic transfer. Nevertheless, on the surface, metallic nanoparticles are susceptible to corrosion. Instead, by encapsulating individual nanoparticles, they are protected. Among the carbon nanostructures, the most common are graphene, carbon nanotubes (CNTs), and carbon nanospheres (CNSs). Unlike CNTs and CNSs, graphene is difficult to obtain in mass production, limiting their applications. Regarding CNTs and CNSs, the latter presents better catalytic activity. Nonetheless, the process of synthesis of CNSs with metal inside is commonly made by time-consuming autoclave processes, some involving more than 43 h, and hence are expensive. Here, we suggest an advantageous synthesis of CNSs with an iron–nickel alloy encapsulated inside, by using a one-step chemical vapor deposition (CVD) process in less than 3 h. This material has potential applications for environmental and energy processes. According to the authors, the uses of iron-nickel alloys as an electrocatalyst for the ammonia oxidation reaction has not been proved. Thus, we evaluate the composite as an electrocatalyst for the ammonia oxidation reaction, an electrochemical process that offers environmental remediation and hydrogen as a fuel. The electrochemical characterization shows that the use of a bimetallic electrode improves the catalytic activity. In this case, nickel is the active specie and iron is the metal added which reduces the reaction potential. Besides, the composite presents high specific capacitance, better than other materials proposed such as graphene decorated with FeNi alloys. This behavior can be related to the variation of the catalyst morphology (supported vs. encapsulated) by improving the catalyst dispersion and particle size stabilization.

Highlights • Conventional pasteurization drastically decreases Lactobacillus sp. • Thermosonication (TS) for less 9 min is sufficient for processing pulque. • Physicochemical properties of pulque were not modified by the use of TS. • Thermosonication extending shelf life of pulque up to 24 days. • TS is a viable technology for processing pulque., The aim of this study was to evaluate thermosonication as an alternative method for the pasteurization of pulque in order to improve its shelf life and retain its quality parameters. Thermosonication was carried out at 50 °C using amplitudes of 75% (for 6 and for 9 min), 85% (for 4 and for 6 min), and 95% (for 3 and for 5 min). These were the optimal conditions found for processing pulque by thermosonication. Physicochemical (acidity, color, alcohol content, and sensory analysis) and microbiological (lactic acid bacteria and yeasts) parameters were determined during 30 days for storage at 4 ± 1 °C. Conventional pasteurization (63 °C, 30 min) and raw pulque were used as controls. According to the results, the shelf life of pulque was extended up to 24 days storage at 4 °C. After this time, the quality of beverage decreased, due that the microbial load increases. Thermosonication treatments at 75% and 85% showed a higher content of LAB (6.58–6.77 log CFU/mL) and yeasts (7.08–7.27 log CFU/mL) than conventional pasteurization (3.64 log CFU/mL of LAB and 3.97 log CFU/mL of yeasts) at 24 days of storage. Raw pulque demonstrated up to 7.77 log CFU/mL of yeasts and 7.51 log CFU/mL of LAB. Pulque processed by thermosonication exhibited greater lightness, sensory acceptance, a maximal acidity of 0.83 g/lactic acid, and an alcohol content of 4.48–4.95% v/v. The thermosonication process preserves sensory and physicochemical properties better than conventional pasteurization. Lactic acid bacteria such as Lactobacillus kefiri, Lactobacillus acidophilus, and Lactobacillus hilgardii and yeasts such as Saccharomyces cereviasiae were identified in thermosonicated pulque.

The reduction of total Pt-loading in a cathode catalyst without sacrificing performance is one of the key objectives for the large-scale commercialization of proton exchange membrane fuel cell (PEMFC) technology. A core-shell type nanostructured catalyst with a Pt-loading 20 times lower than a commercial catalyst is demonstrated herein to be more active for the electrocatalysis of the oxygen reduction reaction (ORR) in acid electrolyte. The weight ratio of metal nanoparticles on carbon support is the key to achieving the highest ORR activity in a series of silver-based catalysts, all with 10 mol percent of Pt and 10 mol percent of Pd over 80 mol percent of silver (Ag) and supported on untreated Vulcan carbon to form an electrocatalyst (Ag@Pt10Pd10/C) with either 5, 10, 20 or 30 wt% of total metals on carbon; which correspond to a Pt concentration around 1, 2, 3 and 5 wt%, respectively. All metal nanostructures on carbon show a similar morphology, size and structure. Thin films of these four Ag@Pt10Pd10/C catalysts on rotating disk electrodes (TF-RDEs) all shown a 4-electrons pathway for the ORR and give higher exchange current densities (jo > 3.8 mA/cm2) than a commercial Etek Pt20/C catalyst (jo = 2.4 mA/cm2). The Ag@Pt10Pd10/C catalyst with 5 wt% of total metals (1 wt% of Pt) on carbon gives the best electrocatalysis; reducing molecular oxygen to water two times faster and generating 25% higher current per milligram of platinum (mass activity) than the commercial catalyst (Pt20/C). Therefore, the Ag@Pt10Pd10/C catalyst with 5 wt% of total metals is a new catalyst for ORR for a PEMFC with a lower Pt loading and cost.

The effect of dough formation using dynamic rheology, thixotropy, zeta-potential, and FT-IR properties of soft wheat dough as a function of Ca(OH)2, and Ca-salts contents (0.3%, 0.7%, and 1.1%) was investigated. Physical data were further supplemented by measurements of dough texture profile analysis, wet gluten, and pH. Additional information provided by structure-sensitive properties, such as the zeta-potential, thixotropic index, and slopes of rheo-destroyed and complex viscosity curves using Cox–Merz rule, can comprise complementary instances of evidence of the ability of dough self-regeneration or build-up after rheodestruction to certain limits. There is a different behavior of the dough properties above and below pH 7.0. Above pI ≈ 5.2, dough (pH 5.5–7.0) has zeta-potential with negative charge from ionizing hydroxyl groups of starch and proteins that favor protein unfolding and that increase α-helix, wet gluten, and functionality. Weak non-covalent bonds and electrostatic forces induce strong entanglement and interaction with water, increase swelling, and preserve the chemical structure. However, at pH > 7.0, Ca(OH)2 treatment changed to negative charge tendency of the dough system, specifically of starch. The effects provided by nixtamalization are essential for its application in improvement of wheat flour with limited functionality, such as soft wheat flour and other grains or materials.

A CoNi-decorated-Pt (40:40:20 wt%) electrocatalyst was theoretically studied and experimentally validated for the oxygen reduction reaction (ORR) in acid media. To predict the activity of the electrocatalyst a Co 16 Ni 16 -decorated-Pt 3 cluster was employed. The O and O 2 adsorption energies were used as descriptors of the catalytic activity for the ORR. All calculations were performed using the density functional theory approach as implemented in the deMon2k code. A combined synthesis of high energy milling-galvanic displacement was performed to produce the CoNi-decorated-Pt electrocatalyst. The physical characterization of the electrocatalyst was developed using X-ray diffraction (XRD) for the phases identification, energy disperse X-ray spectroscopy (EDX) for compositional analysis and scanning transmission electron microscopy (STEM) to determine morphology and particle size of the synthesized electrocatalyst. Cyclic voltammetry and rotating disk electrode techniques were used for the electrochemical characterization of the synthesized electrocatalyst. The O and O 2 adsorption energies showed that CoNi-decorated-Pt (Co 16 Ni 16 –Pt 3 cluster) electrocatalyst represents an attractive candidate for the ORR. STEM micrographs showed homogeneous nanocrystalline particles of 5–10 nm size. The CoNi-decorated-Pt nanoparticles presented high specific activity, 40% above of the determined from Pt/C and similar mass activity from the same commercial Pt/C, used as comparison. Electrochemical results confirm the feasibility of a combined synthesis method to produce nanocatalysts which exhibit similar catalytic activity than that of commercially available Pt/C electrocatalyst.

High energy milling in combination with galvanic displacement were used for the preparation of bimetallic nanocatalysts. Co and Ni monometallic powders milled for 30 and 20 h, respectively were both produced in air atmosphere and used as precursors for the preparation of M-Pt (M = Co,Ni) compounds. Nanosized monometallic powders were physically supported on Vulcan carbon, and covered with 20 wt%Pt through a Galvanic Displacement Reaction (GDR) to produce Co-20Pt/C and Ni-20Pt/C electrocatalysts. XRD was used for phase identification on milled powders and for demonstrating structural transformations of Co powders during milling. Results on unmilled metallic Co powder show a predominant HCP structure modifying to a FCC structure after milling. Ni powders maintain their same FCC structure. Energy Dispersive X-Ray Spectometry (EDX) was used for chemical composition analysis on milled powders at several milling times. Scanning Transmission Electron Microscopy (STEM) show the formation of heterogeneous particle with ∼10 nm in size for both electrocatalysts. The electrocatalytic activity was evaluated by Cyclic Voltammetry (CV) and steady state Rotating Disk Electrode (RDE) for the Oxygen Reduction Reaction (ORR) in 0.1 M HClO 4 . The kinetic parameters on Co-20Pt/C conducted to the highest mass activity for the cathodic reaction.

Here it is proposed the use of nickel supported on carbon nanotubes and carbon nanospheres as a cheaper catalyst alternative to the platinum electrodes for the oxidation process of ammonia. Using scanning electron microscopy and Raman spectroscopy confirmed the presence of the Ni on the surface of the carbon nanostructures and based on the electrochemical results is established that the redox process between Ni+2 and Ni+3 plays the role of intermediate in the ammonia oxidation reaction. This process causes an increment in the anodic current density that is dependent on the pH and ammonia concentration. Even more, using the rotating disk electrode technique, the ammonia oxidation, is defined as a diffusion-controlled process that follows first-order kinetics in respect of the concentration of ammonia and suggests the formation of nitrogen as the principal reaction product, where the carbon nanospheres present the best results.

In the present research work, esterified nanoparticles with 2-octen-1-ylsuccinic anhydride were synthesized from waxy corn starch, to our knowledge for the first time, in a single step of ultrasonic treatment. First, the ultrasound time to produce non-esterified nanoparticles was studied. The results showed that non-esterified nanoparticles had sizes ranging from 63 to 48 nm, as well as polydispersity indexes (PDI) ranging from 0.458 to 0.224 and ζ-potential values ranging from −16 to −24 mV in ultrasonication times ranging from 20 to 100 min. Succinylated nanoparticles were obtained at 80 min with two degrees of substitution i.e., 0.003 and 0.01, hydrodynamic sizes of 57 and 83 nm, PDI of 0.479 and 0.91, and ζ-potential values of −6.27 and −14.03 mV, respectively. The succinylation of nanoparticles was confirmed by FTIR spectroscopy, and it was possible to elucidate the conversion of amylopectin molecules into amylose blocks. The nanoparticles showed stability during storage in aqueous suspension at 4 °C. By means of the ultrasonic technology, destructuring of the waxy corn starch and, at the same time, the succinylation of the nanoparticles in a total time of 120 min was effectively achieved.

Silver (Ag) nanoparticles enriched with platinum (Pt) and palladium (Pd) on their surfaces (Ag@Pt0.1Pd0.1) are supported on Vulcan XC-72 carbon (C) to form a new catalyst (Ag@Pt0.1Pd0.1/C) for the oxygen reduction reaction (ORR) in acid electrolytes. This catalyst is prepared in one pot by reducing Ag and then Pt and Pd metal salts with sodium borohydride in the presence of trisodium citrate then adding XC-72 while applying intense ultrasound. The metallic Ag@Pt0.1Pd0.1 nanoparticles contain 2 weight percent of Pt, are spherical and have an average size less than 10 nm as determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). At the ORR potentials, Ag nanoparticles on carbon (Ag/C) rapidly lose Ag by dissolution and show no more catalytic activity for the ORR than the carbon support, whereas Ag@Pt0.1Pd0.1/C is a stable catalyst and exhibits 1.4 and 1.6 fold greater specific activity, also 3.6 and 2.8 fold greater mass activity for ORR in 0.5 M H2SO4 solution than comparable Pt/C and Pt0.5Pd0.5/C catalysts with the same Pt loading as determined for thin-films of these catalysts on a rotating-disk electrode (TF-RDE). Using silver nanoparticles increases Pt utilization and therefore decreases Pt-loading and cost of a catalyst for a proton exchange membrane fuel cell (PEMFC) electrode.

In the first part of this work, the feasibility of developing a catalyst with high activity for the oxygen electroreduction reaction (ORR) in acid media and with low Pt loading was demonstrated by over coating a silver (Ag) nanoparticle with a shell of platinum (Pt) and palladium (Pd) [7] . The results show that best activity is not directly related to a higher PtPd loading on the surface of the Ag. The best catalyst in a series of this type of catalyst is found with Ag@Pt 0.3 Pd 0.3 /C which gives a specific activity for oxygen reduction, j k (in units of mA cm −2 of real area), of 0.07 mA cm −2 at 0.85 V vs. NHE, as compared to 0.04 mA cm −2 when with a commercial Pt on carbon catalyst (Pt 20 /C) is used in an identical electrode except for the catalyst. The mass activity, j m (in units of mA μg −1 of Pt), for Ag@Pt 0.3 Pd 0.3 /C is 0.04 mA μg −1 of Pt at 0.85 V vs. NHE, whereas that for the Pt 20 /C gives 0.02 mA μg −1 of Pt, showing Ag@Pt 0.3 Pd 0.3 /C is a lower-cost catalyst, because using a Ag core and Pd with Pt in the shell gives the highest catalytic activity using less Pt.

An innovative biolubricant for gears/wheel‐rail systems is formulated; it is produced inexpensively using high‐viscosity vegetable oils modified with additives of unpurified carbon nanopearls (CNPs) and MWCNTs produced via carbon‐vapor deposition. Traditional lubricants made from non‐renewable sources can be replaced with such additive‐based oils. The addition of both unpurified carbon nanopearls and nanotubes containing nanoparticles of Fe, Ni, Co, or SiO₂ is a simple way to improve the tribological properties of biolubricants. Therefore, carbon nanostructures used as additives are not required to be purified or functionalized, thus reducing production costs. Tribological testing is performed with ball‐on‐disc, four‐ball, and twin‐disc machines for two high‐viscosity biolubricants. A complex rosin ester and linseed oil additivated with commercial and raw CNPs/MWCNTs are tested. Scanning electron microscope characterization is used to assess the morphology and structure of both the carbon nanopearls and the multiwalled carbon nanotube particles in addition to the worn metal surfaces. Additionally, X‐ray diffraction, FTIR spectroscopy, and inductively coupled plasma atomic emission spectroscopy are used to characterize the MWCNTs additives. Practical Applications: Biolubricant additivation with raw unpurified MWCNTs and CNPs for enhanced tribological performance. Presence of Fe, Ni, Co, and Si nanoparticles helps fine‐tune the friction coefficient and anti‐wear rates. The proposed method may prove useful in biolubricant formulation for applications in gears/wheel‐rail and metal machining systems.

The present research focused in the feasibility of using a common, inexpensive, and non-toxic material as titanium dioxide (TiO2) for arsenite (As(III)) removal from aqueous solutions. Batch experiments were conducted to test the effects of adsorbent dose, contact time, and stirring speed. The As(III) removal has been carried out under natural environment conditions (temperature 23 ± 3°C and water pH 8 ± 0.2). Results show that the kinetic rate of As(III) adsorption was higher in the first 30 min and decreases thereafter. The maximum removal efficiency was 96% with 1.5 g/L in 1.5 h of contact time. The As–TiO2 system has reached equilibrium in 1 h, regardless of the titanium dioxide dosage. The adsorption process was best described by the Freundlich's isotherm model, which indicates that the multilayer adsorption should be involved in the process of As(III) removal. The contact between the As(III) and TiO2 was done mainly by convection and diffusion. The mass transfer coefficient (β) has been found between 0.8 × 10−5 and 12.3 × 10−5 cm/s. The thermodynamic analysis showed a feasible, spontaneous, and exothermic adsorption process. TiO2 is a safe substance for human health and is a feasible and efficient alternative treatment for arsenic removal from water.Chronic exposures at low-level of arsenic will cause adverse health effects. TiO2 is a feasible low-cost material for remove arsenic. Reaction mechanisms, the zeta potential and adsorption kinetics were analyzed. A dose of 1.5 g/L removed 92% (Co = 120 µg As/L) of arsenic in 0.9 h. This conditions allows to get a treated water quality in agreement with the international standards (

Multiwalled carbon nanotubes (MWNT) modified by 2.2′-azoiso-butyronitrile (AIBN) were incorporated into methyl methacrylate (MMA) by sonochemistry method, resulting in homogenous dispersion of MWNT, which makes possible to obtain flexible conductive polymer-matrix nanocomposites films of PMMA, with MWNT concentrations ranging from 0 to 0.5 wt%. Modified MWNT (AIBN-MWNT) were studied by Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and through visual observations in order to compare the dispersion in 2-propanone and toluene with that of pristine MWNT. Synthesized PMMA-AIBN-MWNT films were studied by FT-IR and Raman spectroscopy. Using FT-IR for the AIBN-MWNT it was not possible to identify any group or groups attached to the nanotubes. Raman spectroscopy shows a small modification in the Lorentzian peaks ratio I D/G of AIBN-MWNT, meanwhile XPS showed that atomic compositions does not change for AIBN-MWNT compared to the pristine nanotubes. Also by impedance it was analyzed the conductivity of PMMA-MWNT films and the results showed a threshold percolation at 0.5 wt%. FT-IR and Raman analyses for PMMA-AIBN-MWNT composite indicate a covalent bonding between PMMA and MWNT due to the opening of π-bonds of the nanotubes, which is related with a possible proposed reaction scheme.

First principles electronic structure calculations based on periodic, self-consistent density functional theory (DFT-GGA) were utilized to study the mechanism of the vapor phase reaction between hydrogen and oxygen on the PdAg(110) alloy surface. The hydrogen–oxygen reaction is an important reaction in the direct synthesis of hydrogen peroxide (H2O2) and at the cathode in proton exchange membrane fuel cells (PEMFCs). Our results demonstrate that the minimum energy path involves the initial formation of a peroxyl (OOH) intermediate followed by O–O bond scission, consistent with the minimum energy path shown on the (111) facet of monometallic Pd and Ag surfaces. The lower activation energy barrier for O–O bond scission in OOH versus hydrogenation of OOH to form HOOH, and the low barrier for HOOH decomposition, suggest that PdAg(110) may not be an effective catalyst for the direct synthesis of H2O2. The detailed thermochemistry and activation energy barriers of important elementary steps and intermediates in...

Different hybrid Ceramic-Polymeric coatings were prepared, from a suspension consisting of a mixture of tetraethyl orthosilicate (TEOS) as a silicon dioxide precursor, polyvinyl acetate (PVA) and colorant to obtain sol-gel SiO2-PVA thin films. The films were prepared using Sol-Gel technology, applied by dip-coating technique. In order to determine the optimal formulation, different samples varying the proportion of PVA were prepared and evaluated. Both optical and mechanical properties were tested, finding an optimal value of 30 percent of PVA for the mechanical properties, and a value of 50 percent for the optimal optical properties. In both cases, the coatings made can be considered as a reasonable alternative for use as a Solar Absorber for Low-Mid range temperature, with a smaller thickness than the comparable commercial coating but with similar performance and lower cost.

High intensity ultrasound was used in the synthesis of PdAg nanoparticles. PdAg nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), scanning transmission electron microscopy (STEM) and high-resolution transmission electron microscopy (HRTEM). Catalytic properties for oxygen reduction reaction (ORR) were determined by electrochemical techniques of cyclic voltammetry (CV) and thin-film rotating disk electrode (TF-RDE). Finally the electrocatalyst was tested as a cathode in a single polymer electrolyte membrane fuel cell (PEMFC). Sonochemical synthesis (SS) decreased the overpotential required for the ORR and increased the double-layer capacitance (DLC) respect to the sodium borohydride reduction method due to a better distribution on vulcan carbon support. The electrocatalytic activity of the nanometric bimetallic electrocatalyst for the ORR in acid media showed a favorable multielectron charge transfer process (n = 4e−) to water formation. The performance of the membrane electrode assembly (MEA) prepared with dispersed PdAg/C as a cathode catalyst in a single PEMFC is lower in comparison to platinum.

In this work, AgxPt100-x/C (x = 60, 80, 90 and 95) colloidal nanostructured electrocatalysts for the oxygen reduction reaction (ORR) were prepared by sequential reduction of AgNO3 and H2PtCl6 using an ultrasound-assisted colloidal method. The synthesized materials were characterized by UV/Vis spectroscopy, XRD, EDS and HRTEM. In addition electrochemical measurements were performed using cyclic voltammetry (CV) and thin-film rotating-disk electrode (TF-RDE) technique in 0.5 M H2SO4 at room temperature. Results of the physical characterization showed ring-like morphology of the nanostructured catalyst with a size distribution in the range of 6-16 nm. From steady polarization measurements, the AgxPt100-x/C nanocatalysts showed electrocatalytic activity towards the ORR like that obtained for Pt/C catalyst under the same experimental conditions and also favored the multielectron (n=4e-) charge transfer process to water formation (i.e., O2+4H++4e- → 2H2O).

The present research is aimed to study the oxygen reduction reaction (ORR) on a PdCu electrocatalyst synthesized through reduction of PdCl2 and CuCl with NaBH4 in a THF solution. Characterization of PdCu electrocatalyst was performed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy. Characterization results showed that the synthesis method produced spherical agglomerated nanocrystalline PdCu particles of about 10 nm size. The electrochemical activity was evaluated using cyclic voltammetry (CV), rotating disc electrode (RDE) and electrochemical impedance spectroscopy (EIS) in a 0.5 M H2SO4 electrolyte at 25 °C. The onset potential for ORR on PdCu is shifted by ca. 30 mV to more positive values and enhanced catalytic current densities were observed, compared to that of pure Pd catalyst. The synthesized PdCu electrocatalyst dispersed on a carbon black support was tested as cathode electrode in a membrane–electrode assembly (MEA) achieving a power density of 150 mW cm−2 at 0.38 V and 80 °C.

Advanced oxidation processes have gained importance in the last decade because of their application in the treatment of wastewater containing toxic, recalcitrant, and/or colored compounds. The catalyst TiO2, activated with ultraviolet (UV) light, has been used for the degradation of different kinds of compounds, but its activation has been performed with different varieties of UV light without a clear reason for choosing any of the three wavelengths that can be generated with commercially available sources. This work evaluates the degradation speed of acid blue 9 dye through the activation of TiO2 with the different kinds of UV light (UV-A, UV-B, and UV-C). The results indicate that the wavelength of the light used for photoactivation has an impact on the dye degradation speed; shorter wavelengths lead to faster degradation. The analysis of the possible causes affecting the degradation speed was performed by superposing the emission bands of the used UV light with the absorption bands of the dye and catalyst. It is concluded that the interaction zone between the type of UV light and the catalyst notoriously impacts the degradation kinetics. © 2011 American Institute of Chemical Engineers Environ Prog, 2011.

Water purification by photo catalytic decomposition of Brilliant Blue colorant in water suspension was studied. This work presents experimental and theoretical results in which the mechanism is discussed of decomposition of an organic colorant’s molecule. In theoretical part, a calculation of the energy levels of the molecule and its parts derived in decomposition process based on modified FEMO modeling confirm the mechanism proposed (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An ammonia-free chemical-bath deposition was used to obtain CdSe thin films on glass substrate. The materials used in the chemical bath were cadmium chloride complexed with sodium citrate and sodium selenosulphate. The preparation conditions, especially the starting solution characteristics, such as concentration of dissolved materials, temperature, pH value as well as deposition time and immersion cycles were optimized to obtain homogeneous stoichiometric films with good adherence to the glass substrate. The films thickness was in the range of 400–500 nm with a growing time of 4 h. The material obtained was characterized by optical absorption, SEM with the energy dispersive X-ray analysis (EDS) and X-ray diffraction. The films obtained at bath temperatures of 70 and 80 °C had the hexagonal structure (of wurtzite type), with crystallite size of about 20 nm. Room temperature deposition results in films with the cubic structure and crystallite size of about 4 nm. From optical transmission data, an energy gap equal to 1.88 eV was found. The material is interesting for applications in hybrid systems for solar energy conversion.

Due to their worldwide availability, glass fibers and aramid fibers have been the more common continuous fibers used to obtain fiber reinforced polymer (FRP) rods. These pultruded rods are used as structural materials and for reinforcements of concrete elements. The main challenge that these fibers face in concrete is their durability in high alkaline environments, therefore the fibers appropriate for this application must be alkali-resistant (AR). In the present work, a cheap Basalt fiber embedded in unsaturated polyester bisphenol “A”-styrene copolymer has been compared to “E” and AR glass fibers under unidirectional tensile strength. A pultrusion process was used to obtain FRP rods. After unidirectional tensile tests of the FRP rods along with durability tests (fibers immersed in a highly alkaline solution at constant temperature simulating the concrete pore solution), the FRP rods with basalt fibers showed to be a cheap and good alternative to be used in concrete.

Tensoactive agents may decrease water absorption in clay products like adobes. They modify the characteristics of the surface of clay particles. Characterization of water diffusion through the pores of modified clays is important to apply appropriate surface modifiers and to improve their performance. We established a simple model for water diffusion in test samples of defined dimensions to estimate real physical parameters and their effect on water absorption. Adsorption mechanisms are examined based on experimental results. The fitting of the experimental data to the model provides a deep understanding of water adsorption in chemically modified clays. A better agreement between the model and the experimental data is achieved for complex molecules.

Availability, cheapness and thermal insulation properties give adobe an advantage over other building materials in dry regions. On the contrary, its poor compressive strength and high water adsorption are important disadvantages. We report the enhancement on compressive strength and water absorption resistance obtained in this material by the addition of dodecylamine and emulsified asphalt to the clay used for its manufacture. We characterized the adobes by X-ray diffraction, infrared spectrometry, ζ-potential measurements and scanning electronic microscopy. Ultra violet accelerated test, compressive strength test and water absorption tests were also carried out. The results show that adobes with cationic amine and emulsified asphalt improve their compressive strength and lower their water absorption at the time that they preserve their properties under weathering conditions.

Data are presented on the coloring conditions, colored layer parameters, and color characteristics of stainless steel 304 samples treated in an electrolytic cell (60 Hz, 100 mV) using a mixture of 5 M sulfuric acid and 2.5 M chromic acid. Reflectance spectra indicate that the samples have high-purity color mainly in the yellow region and that the color is due to interference oscillations in the visible range. In addition, reflectance data in conjunction with composition-depth profiles obtained using glow discharge spectrometry indicate that the coloration of the samples is due not only to reflectance oscillations but also to the subtraction effect. The reduced Fe content and significant oxygen content in the near-surface region attest to the formation of a mixed oxide layer. Atomic-force microscopy examination indicates that the sample surface has an island structure.

Although several processes have been developed to obtain ceramic coatings, many of them are complex, and expensive equipment is required. As an alternative process, in this work, electrodeposition was used to deposit silica on stainless steel substrates. The properties of commercial silica were changed by adding some chemical compounds. Potassium hydroxide was added to promote, in a controllable way, the formation of a silicate network to obtain good adherence on metallic substrates. The addition of reagents caused controlled destabilization on suspension and promoted the formation of clusters. The application of an electric field to obtain coatings allowed the orientation of charged particles and, hence, the properties of the deposited material to be modified. Electrokinetic parameters, electrical response, and GDS profiles were measured to determine the influence of electric field on the coatings.

Two nanostructured Sol-Gel composite materials for application in solar cells engineering were created and studied: the TiO 2 /SiO 2 films for antireflecting coatings of cells, and PMMA/SiO 2 insulating layers on metal substrate for efficient heat extraction from a cell. Structural and optical investigation of the first composite proved that its parameters are adequate to serve the purpose; when doped with the dye absorbing UV light and emitting in the visible, it could also increase quantum yield of a cell. The second composite is designed for use in a hybrid PV/Thermal system, where it could optimize the heat exchange between a cell and solar plane collector, which also leads to an increase of efficiency of the system.

A more flexible organic–inorganic composite material with low density has been obtained using low cost and flexible latex, SBR latex in a gypsum matrix. Because of this, the microstructure and flexural properties of the new composite were studied. It is shown how, by the addition of the SBR latex in the gypsum matrix, either a polymer network (PN) or a thin polymer film is developed between the gypsum crystals increasing the elasticity or flexural behavior of normal gypsum.

Two sets of silica-based coatings have been prepared using two different wet methods. Set A was obtained using the conventional sol–gel method from thetraethyl-orthosilicate (TEOS) as the main precursor. Set B was produced from commercial colloidal silica added with two structural modifiers, KOH and sodium metasilicate (Na 2 SiO 3 5H 2 O). The structure of both sets of coatings was characterized using infrared absorption, X-ray diffraction and nitrogen adsorption isotherms measurements. The results show a much lower surface area and a slower oxygen diffusion rate for coatings of set B, indicating that these coatings have a denser structure and therefore are more effective as oxygen barriers.

SiO 2 based glasses added with nanometric-silver particles have been prepared by the traditional sol–gel process, using the tetraethyl-orthosilicate alkoxide. The Ag particles were prepared using a new method described in this article, the method uses a cementation reaction between Ag ions and an iron electrode. The size of the particles, measured in the dried glass, was in the range of 100–200 nm. The observed structural changes depend on the annealing conditions, such as the annealing temperature, the amount of silver particles and the type of acid (HCl or HNO 3 ) used to catalyze the hydrolysis/condensation reactions during the sol–gel process. Samples prepared using both acids crystallized into the cristobalite phase after thermal annealing at 800 °C. The amount of SiO 2 crystallized depends on the amount of Ag present in the glass. Samples prepared from solutions catalyzed with HCl acid show the formation of nanometric Ag particles after thermal annealing at 500 °C, these small particles are not observed after similar treatments when HNO 3 is used as the catalytic acid. HCl and Ag 2 O form AgCl which is reduced by residual carbon to form Ag ultrafine particles. The diffusion of the reduced Ag spices, which form these particles, is facilitated by the opened structure of the glasses added with Ag, as indicated by IR measurements.

The hybrid PV–thermal system was studied, with the photovoltaic panel (PVP) area much smaller than that of the solar collector. Performance of the different panels in the system was investigated, in particular, those made of crystalline (c-) Si, α-Si and CuInSe2 as well as different materials and constructions for the thermal contact between the panel and the collector. Our conclusion is that the PVP for application in a hybrid system needs a special design providing efficient heat extraction from it. PVP was designed and made. Its study has shown that this design provides the high electrical and thermal efficiency of the hybrid system.

Colloidal silica coatings were deposited on copper substrates and their structural properties and corrosion resistance to a saline solution were studied. Optacol™ colloidal silica was used as primary reactive. Coatings were obtained by immersion and withdrawal speed was 2.1 mm/s. They were dried at 100 °C during 15 min and given a heat treatment at 180 °C for 30 min. X-ray diffraction (XRD) showed the existence on the coating of a semicrystalline cristoballite phase depending on the heat treatment temperature. X-ray-photoelectron spectroscopy (XPS) demonstrated that the formation of SiO2 bonds is enhanced when the heat treatment temperature is increased. Electrochemical impedance spectroscopy (EIS) was used to measure the corrosion resistance of these films.

Colored SiO2 coatings were prepared using the sol-gel process. The color was obtained by adding organic dyes to the starting solutions. The dyes incorporated were the Brilliant Blue, Brilliant Black, Fast Green, Yellow 5, Tartrazine, and Erythrozine. It is observed that mechanical treatment of the starting solution using ball milling reduces the size of aggregated dye particles in the coatings. The material obtained reveals an efficient photoluminescence in the visible and infrared regions of the spectrum. Investigations of the optical absorption, luminescence excitation, and emission spectra show that each of these systems is characterized by a well-defined set of discrete electronic energy levels. A relation is found between the level separation and the structure of the colorant’s molecule and also with the doping level. Besides, the size of the molecular aggregates greatly influences the efficiency of light absorption and emission. It is shown that a simple quantum-mechanical description of the system, treating the organic molecule as a two-dimensional potential well, accounts for the observed optical transitions. The results from this simple approach are compared with those obtained using the modified FEMO and LCAO approaches. A reasonable agreement of theory with experiment was obtained. From this work it is concluded that, by using the sol-gel technique, it is possible to produce systems in which nanometer-scale potential wells are embedded in a SiO2 matrix. The discrete energy levels of the wells correspond to the molecular electronic transitions active in the visible region.

Molecules of the organic colorants were encapsulated in SiO2 glass derived by the solution-gelatinization process; as the result, the colored glass was obtained containing the colorant embedded within the glass in a molecular or molecular aggregates form. The system thus prepared manifests an efficient photoluminescence; the optical absorption as well as the photoluminescence excitation and emission spectra reveal the existence of sets of the discrete energy levels. The structure of the colorant’s molecule and the percentage of doping determine the level separation; the dependence upon the environment is relatively small. The quantum mechanical description of the system is given considering the organic molecules as the two-dimensional quantum wells, with the boundary conditions taking account of the finite depth of the wells and the existence of aggregation. The results of calculations agree with the experiment.

Organic dye molecules (macrilon yellow) were embedded into silicon dioxide matrix by the sol–gel method. Optical measurements at room temperature of absorption and emission were performed at different steps of the gelation process, starting when the suspension was liquid and finishing when it got the solid state. Optical absorption spectra show the dependence with gelation process and with the milling process. The intensity of the absorption band at 420 nm increases with the viscosity of the suspension. This effect is more important for the milled suspension, working with the same pigment concentration. The gelation and the milling processes also affect the emission spectra. The emission spectra has two bands centered at about 520 and 560 nm. During gelation the relative intensity of the band at about 560 nm increases respect the band at about 520 nm. The emission band of the sample made with milled suspension is three times more intense than that of the not milled suspension.

SiO 2 amorphous thin films containing two different concentrations of copper-based colloidal particles were prepared by the sol–gel method. Thermal treatments in air at 350°C result in the segregation of cupric oxide particles. Subsequent reducing treatments in a CO atmosphere at 300 and 500°C for one hour partially reduces the cupric oxide into particles with metallic copper as the main component. The optical properties of the reduced films were characterized measuring the optical absorption spectra as a function of the elapsed time after the reduction process. The absorption data were analyzed in terms of the Mie model for colloidal systems. The fitting of this model to the experimental data provides the temporal evolution of the volume fractions of the three components of the colloidal particles, that is; Cu, Cu 2 O and CuO. It is found that the exposure to air of the films treated at 300°C under the reducing atmosphere, results in a gradual reoxidation of the colloidal particles modifying their chemical composition and therefore the optical properties of the composite film. On the other hand, the reduction treatment at 500°C results in the stabilization of the composition of the colloidal particles, producing stable films with a high optical density.

SiO2 Glasses with incorporation of either Cu or Fe were prepared by the sol-gel process and annealed in air at temperatures within the range of 100 to 500°C. The samples were characterized using Visible Photoacoustic Absorption Spectroscopy (PAS), X-ray powder diffraction and Electron Paramagnetic Resonance (EPR). Under the annealing both systems show significant changes in composition, producing an evolution in the optical absorption spectra. In both systems, the formation of the metal oxide particles is observed after annealing at or above 300°C. The optical and EPR spectra are interpreted in terms of the coordination of the metal ions using the ligand field theory. It is observed that the color of the samples has strong change with both the type of metal incorporated and with the annealing temperature.

Using the sol–gel process SiO 2 coating and powdered samples doped with different concentrations of copper were prepared. Two sets of samples were made: one was thermally treated in air atmosphere, and the other, was annealed under a CO atmosphere. Both sets of samples were characterized using X-ray diffraction, optical transmission spectroscopy, photoacoustic absorption spectroscopy (PAS) in the visible and near infrared region and electron paramagnetic resonance (EPR). It is found that the chemical state of the copper depends on the type of treatment, amount of copper and the temperature of the treatment. The formations of CuO or Cu colloidal particles occur after the thermal treatments in air or in the CO atmosphere, respectively. In both cases, copper is found in the Cu 2+ state in interstitial positions and probably substituting the Si atoms in the SiO 2 matrix. The evolution of the optical absorption spectrum as function of the Cu content is a consequence of the changes in the composition and size of the colloidal particles. The optical and the PAS measurements are found to be complementary tools to elucidate the origin of the blue band in the absorption spectrum of these doped samples.

SiO 2 coatings prepared by the sol-gel method containing various amounts of copper have been annealed under two different atmospheres to produce colloidal copper based particles embedded in a SiO 2 matrix. The particle composition depended on: the amount of copper added to the stating solutions, the atmosphere in which the samples were annealed and the annealing temperature. The optical properties of the colloidal coatings were determined using the model proposed by Mie, using effective values for the optical constants of the colloidal particles.

The current research work presents a methodology for determining the area of influence of the ultraviolet light emitted by a lamp located in the center of a photocatalytic reactor, at different concentrations of the catalyst TiO2 degussa P25 and of the acid blue 9 dye. The measurements for the development of the corresponding methodology were performed through a novel system that allows the evaluation of light intensity at different distances from the lamp and at real working concentrations (with no dilution). The results obtained from these measurements indicate that for 600 mg L−1, 450 mg L−1, 300 mg L−1, and 150 mg L−1 catalyst concentrations there is complete absorption of the light emitted by the lamp at distances of 0.8, 1.0, 1.6, and 2.4 cm, respectively. For the dye it was observed that at 2.4 cm from the lamp, there is an intensity reduction in the order of 91%, 85%, 71%, and 50% for concentrations of 80 mg L−1, 60 mg L−1, 40 mg L−1, and 20 mg L−1, respectively. The results obtained with the application of the developed methodology for the evaluation of the combined effect of the catalyst and dye absorption, show that, the absorption of the catalyst is more important than that of dye in the concentrations evaluated. With higher catalyst concentration, complete light absorption happens closer to the lamp wall, which produces an increment in the reaction kinetics; with higher dye concentrations, the amount of energy reaching by the catalyst decreases and causes an exponential decrease in the reaction kinetics. © 2009 American Institute of Chemical Engineers Environ Prog, 2010

Surface Enhanced Raman Scattering of graphite deposited on Al, Cu and Fe surface has been observed. Ultrathin layers of graphite consisting of only a few carbon monolayers were deposited using a chemical method. Comparing the graphite Raman intensity from these ultrathin layers with those obtained in thicker carbon samples on glass substrates deposited using the sputtering method, the enhancement intensity factor has been determined.

SiO/sub 2/ thin colored films were produced by the solution-gelatinization technique with addition of organic colorants to the initial solution. Colorants made for the food industry (in particular, Brilliant Black, Rhodamine 6GDN and red No. 3 or erythrozine) were used in the powder form; to influence the size of the powder grains, special mechanical treatment (ball-milling) of the solution was performed. All types of the material obtained reveal an efficient photoluminescence in visible and near infrared parts of the spectrum. We found that each of the systems made possesses a definite set of discrete energy levels, which is determined by the structure of the colorant molecules; besides, the efficiency of the light absorption and emission as well as the light stability of color are affected by the mechanical treatment mentioned above. A quantum mechanical description of the systems studied was attempted, treating the organic molecules as the two-dimensional quantum wells; it shows a reasonable agrement with experiment.

In this work a chemical vapour deposition (CVD) process was implemented and automatized for the synthesis of carbon nanotubes (CNTs). Looking the possibility to make an extensive use of biogas, and also for decreasing the costs of the process, methane was used as carbon source. Different CNT structures were obtained using Fe, Ni, Co and also Mo nanoparticles, supported on silica-gel as catalyst for CNT's growing. The number of walls, the morphological effects and efficiency of the process showed dependency on the catalyst type. Cobalt helps the growing of CNTs with fewer layers, compared with Ni, Fe and Mo. Low quality structures are mainly obtained with Fe nanoparticles. Cobalt promotes small diameters in carbon nanotubes and Ni promotes the best quality and yielding during the CVD process.

The SiO 2 glasses obtained by the sol-gel process, doped with Fe or Cu and annealed either at oxidizing or at reducing (CO - CO 2 ) atmosphere, exhibit deep coloring caused by the absorption and scattering bands in the visible spectral region followed by a considerable change of the shape of the infra-red absorption bands in the region 1000 - 1250 cm -1 corresponding to the optical phonon's excitation. An analysis is made of the spectra obtained by the optical and photoacoustic as well as by the Raman techniques; results are compared with the theory taking into account the light absorption and scattering for the visible region and the influence of the phonons' scattering on the shape of the corresponding absorption bands for the infra- red region. We found that the coloration caused by the annealing of the doped glass at 100 degree(s)C is basically due to the individual Cu and Fe ions in interstitial sites. After annealing at 300 degree(s)C and higher temperatures in oxygen atmosphere the doping atoms enter substitutionally for Si; part of them form colloidal particles of the corresponding metal oxide. The latter exhibit both absorption and scattering which determine the glass color. Annealing under reduction conditions leads to the formation of Cu and Cu 2 O particles producing a deeper coloration; interaction of the former particles with carbon (graphite) coating causes a specific changes in the Raman spectra which could be attributed to the SERS - Surface Enhanced Raman Scattering.