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Mediante el desarrollo de un diseno factorial 2k se evaluo la temperatura y concentracion del catalizador en la reaccion para la obtencion de esteres metilicos de acidos grasos (FAME) utilizando aceite residual como sustrato metanol como aceptor de acilo Candida antarctica Lipasa B como catalizador y tamices moleculares como agente secante. Los datos experimentales se analizaron con un analisis de varianza (ANOVA). Las relaciones optimas de catalizador-temperatura se determinaron a 13% -30 ° C, 14,5% -34 ° C y 14% -35 ° C. No se detecto ningun efecto de los tamices moleculares en el rendimiento de la reaccion. Por el contrario, se registro para la acidez del producto, que mostro una disminucion significativa, de 0,79 a 0,40 mg KOH / g. Aplicando las reglas de mezcla, se calcularon las propiedades fisicoquimicas de los FAME (densidad, gravedad API, viscosidad cinematica, punto de enturbiamiento, presion de vapor, indice de cetano y capacidad calorifica). Los resultados establecieron que el biocombustible es apto para uso comercial y cumple con las regulaciones para biocombustibles: ASTM D6751 y EN-14214. Se determino que el terc-butanol es el disolvente optimo para la recuperacion y reutilizacion de la lipasa. Referencias Aca, M., Campos, E., & Sanchez, O. (2009). Estimacion de propiedades termodinamicas de los compuestos involucrados en la produccion de biodiesel. Superficies y Vacio 22, 15-19p. Acevedo, G., & Guardo, A. (2012). Prediccion de las emisiones generadas en la combustion del biodiesel a partir de la microalga chlorella nativa (Tesis de licenciatura). Universidad de Cartagena, Colombia. American Society for Testing and Materials, ASTM (2008): Annual Book of ASTM Standards: Section 5 - Petroleum Products, Lubricants, and Fossil Fuels. ASTM International, West Conshohocken. Araujo, J. (1995). Oxidacao de Lipidios. Imprensa Universitaria. Azocar, L. (2010). Proceso enzimatico para la produccion de metil esteres de acidos grasos utilizando aceites residuales de fritura en mezcla con aceite de raps como materia prima (Tesis doctoral). Universidad de la Frontera, Chile. Baeza-Jimenez R., Lopez-Martinez L.X., and Garcia H.S. (2014). Biocatalytic modification of food lipids: reactions and applications. Revista Mexicana de Ingenieria Quimica. Vol. 13, no.1, 29- 47. Blangino, A., & Romano, S. (2004). Modelado y correlaciones en biodiesel. Anales AFA 16. Chen, H., Ju, H., Wu, T., Liu, Y., Lee, C., Chang, C., Shieh, C. (2011). Continuous Production of Lipase-Catalyzed Biodiesel in a Packed-Bed Reactor: Optimization and Enzyme Reuse Study. Biomedicine and Biotechnology J., 6p. Chieh, Y. (2011). Selection of prediction methods for thermophysical properties for process modeling and product design of biodiesel manufacturing. Instituto Politecnico de Virginia, USA. Du, W., Li, W., Sun.T., Chen, X., & Liu, D. (2008). Perspectives for biotechnological production of biodiesel and impacts. Appl Microbiol Biotechnol, p. 331-337. Fukuda, H., Tamalampudi, S., Talukder, M., Hama, S., Numata, T., & Kondo, A. (2008). Enzymatic production of biodiesel from Jatropha oil: A comparative study of immobilized-whole cell and commercial lipases as a biocatalyst. Biochem Eng J 39:185-189., 185-189p. Gonzalez, M. (2013). Produccion de biodiesel mediante el uso de lipasas y algas. Monografia, Faculdad de Ingenieria y Ciencias Quimicas, Universidad Veracruzana, Mexico. Lee, M., Lee, J., Lee, D., Cho, J., Kim, S., & Park, C. (2011). Improvement of enzymatic biodiesel production by controlled substrate feeding using silica gel in solvent free system. Enzyme and Microbial Technology, 402-406p. Metha, P., Anand, K., & Sharma, R. (2011). A comprehensive approach for estimating thermo-physical properties of biodiesel fuels. Applied Thermal Engineering 31, 235-242p. Pancreac Quimica (s.f). Metodos oficiales de analisis aceites y grasas. Pancreac Quimica. Reid, R., & P, J. (1977). The properties of gases and liquids. New York: McGraw Hill. Rivera, A. (2013). Caculo de las propiedades fisicoquimicas del biodiesel y sus mezclas con diesel a partir de reglas de mezclado (Tesis de Licenciatura).Universidad de Cartagena, Colombia. Rochaya, D. (2007). Numerical simulation of spray combustion using Bio-mass derived liquid fuels (Tesis Doctoral). Cranfield University, Reino Unido. Samukawa, T., Kaieda, M., Matsumoto, T., Ban, K., Kondo, A., Shimada, Y., Fukuda, H. (2000). Pretreatment of immobilized Candida antarctica lipase for biodiesel fuel production from plant oil. J Biosci Bioeng 90, 180-183p. Salazar-Leyva J.A., Lizardi-Mendoza J., Ramirez-Suarez J.C., Garcia-Sanchez G., Ezquerra-Brauer J.M., Valenzuela-Soto E.M., Carvallo-Ruiz M.G., Lugo-Sanchez M.E. y Pacheco-Aguilar R. (2014) Utilization of chitin and chitosan based materials for protease immobilization: stabilization effects and applications. Revista Mexicana de Ingenieria Quimica, Vol. 13, No. 1, 129-150 Saqib, M., Mumtaz, M., Mahmood, A., & Abdullah, M. (2012). Optimized Biodiesel Production and Environmental Assessment of Produced Biodiesel. Biotechnology and Bioprocess Engineering 17, 617-613p. Sarin, A. (2009). Effect of blends of Palm-Jatropha-Pongamia biodiesels on cloud point and pour point. Energy 34, 2016-2021p. Shimada, Y., Wantanabe, Y., Sugihara, A., & Tominaga, Y. (2002). Enzymatic alcoholysis for biodiesel fue production and application of the reaction to oil processing. J. Mol Catal B: Enzymatic, 133-142p. Zhmud, B. (2014). Viscosity blending equations. Lube.Tech, 92, 1-4p.

Nickel nitride (Ni3N) is known as one of the promising precatalysts for the electrochemical oxygen evolution reaction (OER) under alkaline conditions. Due to its relatively low oxidation resistance, Ni3N is electrochemically self-oxidized into nickel oxides/oxyhydroxides (electroactive sites) during the OER. However, we lack a full understanding of the effects of Ni3N self-oxidation and Fe impurity incorporation into Ni3N from electrolyte towards OER activity. Here, we report on our examination of the compositional and structural transformation of Ni3N precatalyst layers on Ni foams (Ni3N/Ni foam) during extended periods of OER testing in Fe-purified and unpurified KOH media using both a standard three-electrode cell and a flow cell, and discuss their electrocatalytic properties. After the OER tests in both KOH media, the Ni3N surfaces were converted into amorphous, nano-porous nickel oxide/(oxy)hydroxide surfaces. In the Fe-purified electrolyte, a decrease in OER activity was confirmed after the OER test because of the formation of pure NiOOH with low OER activity and electrical conductivity. Conversely, in the unpurified electrolyte, a continuous increase in OER activity was observed over the OER testing, which may have resulted from the Fe incorporation into the self-oxidation-formed NiOOH. Our experimental findings revealed that Fe impurities play an essential role in obtaining notable OER activity using the Ni3N precatalyst. Additionally, our Ni3N/Ni foam electrode exhibited a low OER overpotential of 262 mV to reach a geometric current density of 10 mA cmgeo−2 in a flow cell with unpurified electrolyte.

Electrochemical water splitting is one of the most promising approaches for sustainable energy conversion and storage toward a future hydrogen society. This demands durable and affordable electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In this study, we report the preparation of uniform Ni–P–O, Ni–S–O, and Ni–S–P–O electrocatalytic films on nickel foam (NF) substrates via flow cell-assisted electrodeposition. Remarkably, electrodeposition onto 12 cm2 substrates was optimized by strategically varying critical parameters. The high quality and reproducibility of the materials is attributed to the use of a 3D-printed flow cell with a tailored design. Then, the as-fabricated electrodes were tested for overall water splitting in the same flow cell under alkaline conditions. The best-performing sample, NiSP/NF, required relatively low overpotentials of 93 mV for the HER and 259 mV for the OER to produce a current density of 10 mA cm−2. Importantly, the electrodeposited films underwent oxidation into amorphous nickel (oxy)hydroxides and oxidized S and P species, improving both HER and OER performance. The superior electrocatalytic performance of the Ni–S–P–O films originates from the unique reconstruction process during the HER/OER. Furthermore, the overall water splitting test using the NiSP/NF couple required a low cell voltage of only 1.85 V to deliver a current density of 100 mA cm−2. Overall, we demonstrate that high-quality electrocatalysts can be obtained using a simple and reproducible electrodeposition method in a robust 3D-printed flow cell.

A rapid and sustainable route for synthesizing a green photocatalyst based on nanometric Cu2O clusters dispersed on TiO2 (≈ 2 wt%) was developed. These nanoclusters were synthesized using reducing sugars (0.85 wt%) from aqueous onion waste (Allium cepa) as reducing and stabilizing agent. All this under microwave irradiation. Green photocatalysts produced hydrogen through glycerol photoreforming, ca. 4.7 mmol H2/gcat. The recyclability and reusability of these materials were demonstrated and the achieved heterojunction between Cu2O and TiO2 exhibited a bandgap within the visible spectrum at 2.80 eV, showing potential feasibility to solarize this process.

Sulfur-based thermochemical cycles, such as the hybrid sulfur-ammonia (HySA) cycle, offer a valuable approach in which hydrogen is produced by exploiting sulfur dioxide (potentially pollutant emissions) through the electrochemical oxidation of aqueous sulfite. In this study, the effect of pH on electrooxidation rate was assessed by comparing different reaction scenarios. Then, a Central Composite Design (CCD) combined with a Response Surface Methodology (RSM) was used to optimize batch electrooxidation of ammonium sulfite at near-neutral pH. Results show that the use of an anion exchange membrane (AEM) greatly improves sulfite electrooxidation rate while pH is effectively stabilized. Furthermore, a second-order model that relates applied potential and sulfite concentration with the normalized half-life of the reaction was obtained and verified experimentally at long-term batch electrooxidations. A good agreement between the model and experimental tests, adequate hydrogen recoveries and low sulfur crossover through the membrane demonstrate practical robustness of this approach.

Lactose is commonly crystallized in the presence of whey proteins, forming co-crystals of lactose and proteins. This work hypothesized that flavonoids such as rutin or epigallocatechin-3-gallate (EGCG) could be incorporated into the lactose and protein co-crystal structure since flavonoids may interact with both lactose and proteins. The interactions between whey proteins and flavonoids were first studied. Then, lactose-protein solutions were crystallized with and without flavonoids, measuring the kinetic parameters of crystallization and characterizing the resulting crystals. The incorporation of flavonoids in lactose-protein co-crystals depended on the hydrophilic nature of flavonoids. The hydrophilic EGCG was scarcely enclosed in the crystal lattice of lactose and avoided the inclusion of whey proteins in the crystals. In contrast, the less water-soluble rutin interacted with whey proteins and lactose, leading to the formation of co-crystals containing lactose, protein, and a large concentration of rutin (3.468 ± 0.392 mg per 100 mg of crystals).

Reducing household energy consumption is one of the most important strategies used to decrease fossil fuel consumption and greenhouse gases emissions, and to encourage renewable energy utilization. Most energy conservation strategies in the domestic sector are aimed at preferential loans, i.e., purchasing renewable electricity or to improve the efficiency of home appliances, such as air conditioning and lighting. However, despite the relative economic successes of these technologies, they have not had expected impacts in regard to energy consumption. In this work, the authors analyzed the consumption patterns of two equivalent households—one was adapted with improved thermal insulation and a 1.2 kW photovoltaic system to reduce consumption from the electrical grid. The results show that dwellings where no improvements were made registered lower electric energy consumption, due the fact that users were aware that no strategy had been implemented, and its consumption; hence, electricity payments depended solely on one’s attention over the electronic device operations. On the other hand, energy conservation strategies in households promotes confident and relaxed attitudes toward the use of energy, leading to lower energy billings, but a higher gross energy consumption.

Activated carbons are key electrode materials for supercapacitors (SCs) widely used in commercial devices. Here we investigate the preparation of activated solar carbons (ASCs) from pecan nutshell waste for their use as electrode materials for SCs. The ASCs are prepared using a sustainable process where concentrated solar energy is used as heat source for the one-step carbonization/chemical activation using H3PO4. From physical characterization we observed that our prepared ASCs are amorphous carbons, which have well-developed microporous surface of different features related with a pretreatment of pecan nutshell. The ASCs are electrochemically evaluated by cyclic voltammetry in four aqueous electrolytes using a three-electrode system, obtaining capacitances at 5 mVs−1 of 150 and 129 Fg-1 in acidic (0.5 M H2SO4) and environmentally-friendly neutral (1 M CH3COONa) electrolytes, respectively. Finally, we assembled asymmetric carbon-carbon SC cells showing excellent performance compared to a commercial activated carbon, with capacitances around 30 Fg-1 at 0.5 A g−1 with only ∼10% of capacitance loss after 5000 cycles, reveling a high stability, and a widest voltage window with the 1 M CH3COONa electrolyte. Our study provides a novel sustainable approach to use agricultural waste biomass to produce useful electrode materials for energy storage devices using concentrated solar energy.

Recientemente, la modificación de aceites vegetales para obtener ésteres metílicos de ácidos grasos (FAMEs) o biodiesel ha emergido como una alternativa para la sustitución de los derivados del petróleo, esto debido a los problemas ambientales y de salud que genera su uso. Debido a su estructura química es posible epoxidar estas moléculas y usarlas directamente para producir plastificantes o lubricantes. Sin embargo, éstas también pueden ser sujetas a modificaciones para mejorar sus propiedades y el de servir como intermediarias para la síntesis de poliuretanos. Puesto que los métodos convencionales para la producción de epóxidos también son una fuente potencial de contaminación, se ha sugerido el uso de catalizadores enzimáticos como una alternativa sostenible o “Verde” para su preparación, ya que permiten obtener productos con alta pureza y mejores rendimientos. Este artículo presenta una revisión de la literatura disponible centrándose en la epoxidación enzimática de los FAMEs, así como sus principales aplicaciones.

Thermochemical water splitting cycles (TWSCs) are processes with the potential for large-scale production of carbon-free hydrogen. Among these, the sulfur-family thermochemical cycles are considered the most promising due to both, the use of readily affordable chemical reagents and the temperature required to thermally decompose oxygenated sulfur compounds, which is achievable by solar means. Indeed, solar heat assisted metal sulfate decomposition is a key step, where catalysis can be employed to reduce decomposition temperature. Here we present a green route to synthesize Ag-Pd and Fe-Pd intermetallic alloy catalysts supported over γ-Al2O3 and Si-C by a microwave-assisted method using glycerol both as a solvent and as a reducing and stabilizing agent. The obtained supported catalysts were physicochemically characterized. Fe-Pd/Al2O3 catalyst exhibited the best performance, abating the zinc sulfate decomposition temperature by ca. 85 °C in comparison with other reported catalysts.

Bioelectrochemical systems are devices where organic matter (e.g. wastewater) is oxidized through exoelectrogenic bacteria; this process is a new alternative to energy crisis and to mitigate climate change. If the products of such oxidation are electrons they are called microbial fuel cell (MFC), otherwise if the product is hydrogen these devices are called microbial electrolysis cells (MEC) Mostly, MEC's studies have reported double chamber designs, where the anode and cathode are separated by an ion exchange membrane. Nafion is a proton exchange membrane widely used to study bioelectrochemical devices; however, to our knowledge there are no reports of bipolar membranes (BPM) in these systems. In this study, a double-chambered MEC was constructed to evaluate the performance of the system using Nafion® 117, and FUMASEP® FBM bipolar membrane, separately. Biofilm formation was monitored by cyclic voltammetry and open circuit potential (OCP); maximum power for MFC-Nafion and MFC-BPM were 105.1 and 3.6 mW/m2, respectively. Hydrogen yield and COD removal were significantly different for both MEC systems. Whereas COD removal for MEC-BPM was 44.8%; MEC-Nafion exhibited a COD removal of 87.4%. Solely the latter system produced hydrogen, with a yield of 7.6%.

Er3+/Yb3+ co-doped tellurite glasses (83-x)TeO2–10Nb2O5–5Al2O3–xTiO2–1Er2O3–1Yb2O3 where x=0, 2.5, 5, 7.5 and 10 mol% were fabricated by the conventional melt quenching technique. The structural, thermal and optical properties of the tellurite glasses were studied in dependence of the TiO2 concentration. All samples exhibit an amorphous structure which was modified by the introduction of TiO2 according to the X-Ray Diffraction (XRD) and Raman spectroscopy results. Differential scanning calorimetry (DSC) shows that the glass transition temperature and thermal stability increases with the addition of TiO2. The highest value of glass transition temperature (Tg) was 722 K which is one of the highest values found in the literature. On the other hand, the thermometric properties of two representative samples were studied by the fluorescence intensity ratio (FIR) technique. The maximum sensor sensitivity was 4.48 x 10–3 *K–1 at the 490 K temperature for sample with 5 mol% of TiO2 and 5.94 x 10–3 *K–1 at the 480 K temperature for sample with 7.5 mol% of TiO2 corresponding to 32% increase in the maximum sensor sensitivity by increasing TiO2 concentration. These results suggest that the presented host matrix is a good candidate for high temperature sensing applications.

The electrochemical oxidation of sulfite ions offers encouraging advantages for large-scale hydrogen production, while sulfur dioxide emissions can be effectively used to obtain value-added byproducts. Herein, the performance and stability during sulfite electrolysis under alkaline conditions are evaluated. Nickel foam (NF) substrates were functionalized as the anode and cathode through electrochemical deposition of palladium and chemical oxidation to carry out the sulfite electro-oxidation and hydrogen evolution reactions, respectively. A combined analytical approach in which a robust electrochemical flow cell was coupled to different

It has been reported that polysaccharides like carrageenan can change the crystallization of lactose. However, it is still unclear whether changes in lactose mutarotation, solubility, and super-solubility are involved in carrageenans' effect on lactose crystallization. It has been established that the conversion of α- to β-lactose forms (mutarotation) in an aqueous solution has a significant impact on lactose crystallization. Similarly, lactose solubility changes lead to changes in the metastable zone (MZ), a region between the solubility and super-solubility of lactose. The width of this MZ determines the temperature drop necessary to induce lactose nucleation. This work aimed to study the effect of carrageenans on lactose mutarotation and solubility. For this purpose, lactose solutions were added with ι and κ- carrageenan at two concentrations: 50 and 100 mg L−1. Optical rotation measurements estimated the proportion of β/α isomers in lactose solutions. Besides, solubility and super- solubility was determined to build the MZ. The presence of carrageenans changed both the time to reach the mutarotation balance and the proportion of β/α isomers at mutarotation equilibrium. Carrageenans decreased the solubility of lactose in a range of temperatures between 10 and 60 °C and reduced the metastable zone width (MZW).

Palladium-based electrocatalysts are widely used in alkaline direct alcohol fuel cells. The synthesis and characterization of carbon-supported bimetallic nanoparticles (NP) of AuPd and AgPd is described using pecan nutshell extract (Carya illinoinensis) which serves as both, reducing and the stabilizing agent. This environmentally friendly route generates bimetallic NP for a wide range of applications, including electrocatalysis; since particularly AuPd NP proved to be a potentially suitable electrode material for alkaline direct methanol fuel cells. The electrocatalytic activity of these nanomaterials was comparable to commercially available Pd/C 1% in the electro-oxidation of methanol in alkaline media.

The study evaluated the spatial and seasonal variations of microplastic abundances in water, sediments, and commercial fishes of a semi-urban tourist impacted estuary in the Gulf of Mexico, Mexico. The prevalence of microplastics (MPs) elucidated diffuse sources namely long-range transport, domestic, agricultural, fishing, industrial and recreational activities and the local climatic conditions. Seasonally, the mean abundances of MPs in both water and sediments were high during Nortes (strong winds) followed by the dry and rainy seasons. Overall, black and blue colored MPs dominated the region and all the recovered plastics were fibers. The commercial fishes (n = 187) contained 881 MPs in their gastrointestinal tracts, suggesting that the food web of the estuary is highly prone to microplastic contamination. SEM images of extracted plastic fibers presented surface morphologies that are impacted by physical strains. Further, the elemental characterization of fibers using EDX displayed significant peaks of Al, As, Cl, Cr, Cu, Pb, and Zn that were used as additives during the production of plastics. The main types of polymers included low-density polyethylene, polyester, polypropylene, polycarbonate, rayon, polyvinyl chloride, polyacrylonitrile, polyamide, nylon and polyethylene terephthalate. MP abundances demonstrated in this study elucidate that estuaries are a major conduit for land-derived plastics to the ocean and the results will aid in implementing remedial/clean up actions of the estuary for better conservation of the ecosystem.

Lactose is recovered by crystallization from cheese whey that is a by-product of cheesemaking. The whey used for the recovery of lactose usually has a residual content of protein that alters the crystallization of lactose. In addition, the pH of whey may fluctuate depending on the cheese variety. However, there is little information on how the pH modifies the effect that whey proteins have on lactose crystallization. Accordingly, this work aimed to evaluate the individual and combined effect of whey proteins and pH on the kinetics of crystallization, the crystal size distribution and the crystallinity of lactose. The addition of whey proteins in lactose solutions (25% v/v) modified the process of lactose crystallization. However, the effect that whey proteins had on lactose crystallization heavily depended on the pH. The number of crystals per milliliter as well as the growth and size distribution of crystals was the most affected with the changes in pH (pHs of 7, 5.5 and 4) and the addition of whey proteins (0 and 0.63%). All the treatment produced mostly α-lactose monohydrated but some treatments also generated crystals of β-lactose (pH 5.5, 0% of proteins). Amorphous lactose was observed mainly in lactose solutions adjusted at pH 7 and added with whey proteins. This particular treatment also incorporated the highest amount of protein into the lattice of lactose crystals. The results of this work highlight the importance of controlling the pH of lactose crystallization, especially if there is a presence of whey proteins.

An efficient, general synthetic protocol for the synthesis of the biologically active benzofurans ailanthoidol, egonol and homoegonol was developed. The key starting material, eugenol, is a naturally occurring and abundant precursor. The protocol, involving sequential acylation and intramolecular Wittig reaction, provides a convenient method for building the benzofuran moiety in good yield.

Coal consumption has led to a worrying surge in flue gas emissions, aggravating health and environmental issues worldwide. Therefore, novel approaches supported by sustainable technologies are needed to exploit flue gas emissions effectively. Here, we evaluate an ammonia-based flue gas desulfurization process based on the photochemical capture of CO2 and SO2 for producing hydrogen and ammonium-based fertilizers. The kinetics and mechanistic pathways for sulfite photooxidation are examined, while process feasibility and environmental relevance are evaluated by process simulation and life cycle assessment. Results show that increasing the initial sulfite concentration results in faster reaction rates, following first-order kinetics with an activation energy of 32.9 kJ/mol. Moreover, kinetics is ascribed to two competing photoinduced radical-mediated reaction pathways. Finally, powering the process by renewable energy leads to positive human health, ecosystems, and resources scores in life cycle assessment, supporting the sustainability of the process. Overall, this approach offers essential insights for large-scale hydrogen production through the photooxidation of captured flue gas emissions.

The sulfur-ammonia (S NH3) cycle uses the entire solar radiation spectrum to split water. It uses the UV radiation to promote the photolytic oxidation of ammonium sulfite to produce hydrogen and ammonium sulfate. Here, Raman and inelastic neutron scattering spectra of (NH4)2SO3·H2O at 20 K are discussed, supported by density functional theory (DFT) calculations. The feasibility of photolytic oxidation of this monohydrate to produce hydrogen at room temperature was also demonstrated.

Dietary supplements may contain heavy metals with the property of bioaccumulation in humans. The aim of this research was to validate and apply two analytical methods to determine Pb, As, Cr, and Hg in dietary supplements by Total Reflection X-ray Fluorescence Spectroscopy (TXRF). Methods validation was conducted through a multivariate analysis using a central composite design (CCD) and a desirability function. Critical values for each study variable were established. The TXRF_DS_1 method was proposed for Pb, As, and Cr determinations, while the TXRF_DS_2 was established for Hg analysis. The digestion method with an acid mixture (HNO3 + HCl + H2O2) was used to break down the organic material of dietary supplements. A solution of 10 μg L−1 Ga was used as an internal standard. Excellent analytical performance was obtained as LODs of 0.59, 0.41, 0.57, and 0.75 μg L−1 and LOQs of 1.95, 1.35, 1.90, and 2.50 μgL −1 for Pb, As, Cr, and Hg, respectively. Calibration curves showed a good linearity for all elements (R2>0.999). Excellent accuracy and precision in measurements (% RSD) was achieved. The real and spiked samples analysis demonstrated the applicability of the TXRF technique (percentage recovery 91–108%). Besides, two samples were analyzed in a comparison study between the TXRF_DS_1 method and the ICP-OES method. The results obtained showed good agreement between both techniques. The TXRF technique allows the analysis of toxic heavy metals in dietary supplements, which are marketed in a wide variety of presentations.

Electrochemical oxidation of sulfite ions offers an efficient and profitable approach to the conversion of sulfur dioxide, a harmful air pollutant, into valuable by-products via flue gas desulfurization. Here, the electrochemical oxidation of sulfite in near-neutral pH electrolytes is studied in order to determine kinetic parameters and a reaction mechanism. Sulfite electrooxidation on palladium is demonstrated at pH 7.5 and 8.5, the latter being comparable to platinum. Anodic charge transfer coefficients and non-linear reaction orders are linked to a mechanism which involves sulfite adsorption at low potentials. This study proves that sulfite electrooxidation on palladium at near-neutral pH is a useful approach for sulfur dioxide exploitation. Keywords: Sulfite electrooxidation, Kinetics, Palladium, Reaction mechanism

In this contribution, different porphyrin derivatives were experimentally synthesized and theoretically analyzed using several electronic structure methods to study the geometrical and electronic properties of A4, trans-A2B[Formula: see text]and A3B porphyrins bearing several functional groups (–OH, –COOH, -3,5-di-[Formula: see text]Bu, –OCH2CH2CH2COOEt and –OMe) suitable to be employed as dyes in Dye Sensitized Solar Cells (DSSC). A4 (R [Formula: see text] -H, -OMe, -OH, -3,5-di-tert-butyl, –OCH2CH2CH2COOEt) and A3B (R[Formula: see text][Formula: see text]R[Formula: see text][Formula: see text]R[Formula: see text][Formula: see text]–H; R[Formula: see text][Formula: see text]–OH and R[Formula: see text][Formula: see text]-3,5-di-[Formula: see text]Bu) porphyrins were synthesized and characterized by UV-vis and 1H NMR spectroscopies for comparison. The geometrical parameters were analyzed in the ground state and gas phase using the semiempirical method PM6 and the DFT functionals M06-2X and B3LYP, in combination with the 6-31G(d), DZVP and TZVP basis set. For calculations of the electronic and excited state properties, CAM-B3LYP, M06-2X and HSE06, using SMD as solvation model, were applied. This study revealed that HSE06/DZVP protocol is the best methodology to simulate electronic spectra in these porphyrin derivatives. Indeed, whereas substituent groups did not significantly affect the geometrical structure of the porphyrin derivatives studied, they do influence their electronic structures, mainly in the LUMO (lowest unoccupied molecular orbital) energy levels.

International audience; Carbon fiber-reinforced carbon (C/C) composites consist in a carbon matrix holding carbon or graphite fibers together, whose physical properties are determined not only by those of their individual components, but also by the layer buildup and the material preparation and processing. The complex structure of C/C composites along with the fiber orientation provide an effective means for tailoring their mechanical, electrical, and thermal properties. In this work, we use the Laser Flash Technique to measure the thermal diffusivity and thermal conductivity of C/C composites made up of laminates of weaved bundles of carbon fibers, forming a regular and repeated orthogonal pattern, embedded in a graphite matrix. Our experimental data show that: i) the cross-plane thermal conductivity remains practically constant around (5.3 ± 0.4) W*m−1 K−1, within the temperature range from 370 K to 1700 K. ii) The thermal diffusivity and thermal conductivity along the cross-plane direction to the fibers axis is about five times smaller than the corresponding ones in the laminates plane. iii) The measured cross-plane thermal conductivity is well described by a theoretical model that considers both the conductive and radiative thermal contributions of the effective thermal conductivity.

Lead and chromium contamination represents one of the most serious problems in the aquatic environments. The aim of this work was to develop and validate an accurate, sensitivity, and rapid method for the simultaneous determination of Pb and Cr at trace levels in tissues and fat of marine organisms such as turtle (Chelonia mydas), shark (Rhizoprionodon terraenovae), and dolphin (Tursiops truncatus), utilizing the total reflection X-Ray fluorescence (TXRF) spectroscopy. Working solutions were prepared in 10 mL of a solution 0.005 mol·L−1 EDTA and 1 mol·L−1 HNO3. In order to correct possible instrument drifts, 20 μg·L−1 of gallium was used as internal standard (IS). The results showed that TXRF method was linear over the concentration ranges of 5.242–100 μg·L−1 for Pb and 2.363–100 μg·L−1 for Cr. Limits of detection (LOD) achieved were 1.573 and 0.709 μg·L−1 for Pb and Cr, respectively, while limits of quantification achieved were 5.242 μg·L−1 for Pb and 2.363 μg·L−1 for Cr. The validated method was accurate and precise enough for determination of these heavy metals in samples of marine organisms as indicated by acceptable values of recovery between 90–101%. In addition, a certified reference material (BCR-279, sea lettuce) and a Centrum tablet were satisfactory analyzed, and the T-test for comparison of means revealed that there were no significant differences at the 95% confidence level between the values obtained with the proposed TXRF method and the certificated values. The repeatability of the method, expressed as relative standard deviation (RSD), was 5.1% and 4%, for Pb and Cr, respectively. In addition, other features of the developed method were a low sample volume of 10 μL, and the sample frequency achieved was 20 h−1.

Agriculture is one of most important economic activities that requires large amounts of water, which, in addition to changes in climate, presents a major impact on the water availability. Excess of salt and nutrient concentrations build up damages to soil such as reduced drainage and increase in anoxic conditions in the root zone, as well as decreasing productivity and usable farm lands. The objective of the present study was to evaluate the chemical vulnerability of an aquifer in arid conditions with a high level of extraction through the detection of risk zones and potential subregions of different risks. An evaluation of the quality of the groundwater was performed, as a reconnaissance prior to more detailed studies, in which samples of 30 wells were analyzed to determine physical-chemical parameters (recorded in situ), dissolved chemical species (UV–vis spectrophotometry), and elemental content (X-ray fluorescence spectrophotometry). Concentrations of TDS, as well as Ca, Mg, S, Cl, and As determined in the water under analysis exceeded the limit established for water for consumption and irrigation. It is suggests that the origin of the elemental composition is mainly due to the mineral composition of the aquifer sediments. The wells were classified in three groups located in different zones, based on: a) alkaline earth elements, b) halogens, c) dissolved ions. Water salinity is mainly composed by sulphates and, a lesser extent, by hydrochloric salts from leaching of evaporites. Furthermore, the highest chemical vulnerability are located from central to north zone, where the soils showed crop leaching requirement by above of threshold value for pecan crops, one of the major agricultural products of the valley. In conclusion, both the salinity and the high level of water extraction for agriculture, combined with the arid conditions, are provoking an increase in contents of some chemical species in soil of crops. The immediate consequences are related to a reduction in the agricultural production and, therefore, a decrease in the productive competitiveness.

Concentrating solar power (CSP) systems use solar absorbers to convert sunlight into thermal electric power. In CSP systems, a high reflective surface focuses sunlight onto a receiver that captures the solar energy and converts it into heat. The operation of high efficiency CSP systems involves improvements in the performance of the coatings of the solar absorption materials. To accomplish this, novel, more efficient selective coatings are being developed with high solar absorptance and low thermal losses at their operation temperature. Heat losses in a CSP system occur by three mechanisms: conduction, convection and radiation. It has been widely documented that energy losses increase with increasing operating temperature of CSP systems, and the precise knowledge of the thermophysical properties of the materials involved in CSP systems may allow us to increase the efficiency of systems. In this work, we applied the pulsed photoradiometry technique (PPTR) to evaluate the changes in the thermophysical prope...

This article presents, in summary form, the characteristics of COSOLπ development project and some of the results obtained to date. The benefits of the work of this project will include the generation of a not polluting transportable energy feedstock from a free, abundant and available primary energy source, in an efficient method with no greenhouse gas emission. This will help to ensure energy surety to a future transportation/energy infrastructure, without any fuel import. Further technological development of thermochemical production of clean fuels, together with solar reactors and also with the possibility of determining the optical and thermal properties of the materials involved a milestone in the search for new processes for industrialization. With the above in mind, important national academic institutions: UAM, UNAM, CINVESTAV, UACH, UNISON among others, have been promoting research in solar energy technologies. The Goals and objectives are to conduct research and technological development drivin...

The Au(I)–Au(I) closed-shell or aurophilic attraction has been the subject of interest in the experimental and theoretical chemistry fields, due to the intriguing properties associated to it. The presence of phosphorescence in “aurophilic” compounds has been addressed to a wide range of applications, but it has not yet been fully understood. A theoretical study on the electronic and phosphorescent properties of the following series of dinuclear gold complexes has been performed: [Au2(dmpm) (i-mnt)] (1), [Au2(μ-Me-TU) (μ-dppm)] (2), and [Au2(μ-G)(μ-dmpe)] (3). Full geometry optimizations at the second-order Moller–Plesset perturbation theory (MP2) were carried out for each of the species. These calculations made evident that, at the ground-state geometry, the Au(I) cations allocated at the center of the ring show a short Au–Au distance below the sum of the van der Waals radii, at the range of the aurophilic attraction. An intermolecular Au(I)–Au(I) closed-shell attraction for a pair of the systems under study is found. This attraction is comparable to that of the hydrogen bonds. The phosphorescent properties experimentally observed for this series were also characterized through ab initio techniques. The obtained results allow to fit reasonably the excitation energies with the experimental data and to identify a correlation between the strength of the Au(I)–Au(I) interaction and the phosphorescent behavior. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Solar technology operating at elevated temperature conditions demands accurate knowledge of the optical and thermal properties of the materials involved in the construction and operation of solar collectors, reactors, and energy storages, among many others. Thermal energy storage (TES) devices involve successive melting and crystallization processes, which result in high complexity materials where the morphology, composition, and porosity could be highly non-homogeneous. In these cases, contact techniques for determining the thermal properties are highly susceptible and do not provide reliable measurements. It is under these conditions that non-contact photothermal techniques can provide superior performance, because in this case, the heat inducing source is a laser beam and the detector is usually a photodiode or a thermographic camera which are in non-contact with samples. The materials applied as storage medium in a TES unit can be divided into four groups: metals and alloys, ceramics and glasses, polymers and elastomers, and composites that include natural materials. Soda lime silicate glass recyclable waste is a very promising material for storage medium due to its inexpensive and wide availability. In this paper, we examined soda lime silicate glass-graphite composites for use as storage medium in a TES unit. A simple one-dimensional model for thermal conductivity was developed based on equivalent thermal circuits for series-parallel composite walls, and we found that thermal conductivity values depend on the amount of graphite dispersed into the samples, the porous media, and their structure.

Background Malathion (R,S)-diethyl-2-[(dimethoxyphosphorothioyl)sulfanyl]butanedioate is a chiral organophosphorus compound used widely as pesticide for suppression of harmful insects such as mosquitoes. It is well known that in biological systems (R)-malathion is the active enantiomer, therefore a sustainable approach could be the use of only the biologically active enantiomer. The resolution of the commercial racemic mixture to obtain the pure active enantiomer combined with a recycling of the undesired enantiomer through a racemization process could be an attractive alternative to reduce the environmental impact of this pesticide. Thus, this work evaluates the use of four commercially available lipases for enantioselective hydrolysis and separation of malathion enantiomers from the commercial racemic mixture. Results Several lipases were methodologically assessed, considering parameters such as enzyme concentration, temperature and reaction rates. Among them, Candida rugosa lipase exhibited the best performance, in terms of enantioselectivity, E = 185 (selective to the (S)-enantiomer). In this way, the desired unreacted (R)-enantiomer was recovered in a 49.42 % yield with an enantiomeric excess of 87 %. The monohydrolized (S)-enantiomer was recovered and racemized in basic media, followed by esterification to obtain the racemic malathion, which was recycled. In this way, an enantioenriched mixture of (R)-malathion was obtained with a conversion of 65.80 % considering the recycled (S)-enantiomer. Conclusion This work demonstrated the feasibility of exploiting Candida rugosa lipase to kinetically resolve racemic malathion through an environmentally friendly recycling of the undesired (S)-enantiomer. Graphical Abstract Lipase catalyzed enantioselective resolution of (R)-malathion in aqueous solvent.

A short and practical preparation of α-asarone was developed using the inexpensive methylisoeugenol as a starting material. The utilization of a sequence of tribromination, debromination, and copper-mediated aromatic substitution enabled the stereoselective formation of only the E-isomer of α-asarone in good yield.