Instituto de Desarrollo Tecnológico para la Industria Química

We grow epitaxial graphene monolayers on Ru(0001) that cover uniformly the substrate over lateral distances larger than several microns. The weakly coupled graphene monolayer is periodically rippled and it shows charge inhomogeneities in the charge distribution. Real space measurements by scanning tunneling spectroscopy reveal the existence of electron pockets at the higher parts of the ripples, as predicted by a simple theoretical model. We also visualize the geometric and electronic structure of edges of graphene nanoislands.

Inspired by the use of fatty acids in development of low temperature latent heat storage materials, novel low viscous and hydrophobic deep eutectic solvents (DESs) based exclusively on fatty acids are herein proposed as sustainable solvents. Three DESs were prepared by exclusively combining fatty acids, namely octanoic acid (C8), nonanoic acid (C9), decanoic acid (C10), and dodecanoic acid (C12), which can simultaneously act as hydrogen bond donors and acceptors. The obtained fatty acid-based DESs were analyzed in order to check their structures, purities, and proportions. Water stability was also carefully evaluated through 1H NMR. Fatty-acid DESs melting point diagrams were determined by visual observation. Good agreement was obtained between the experimental eutectic point and that predicted by considering an ideal system of two individually melting compounds. Important solvent thermophysical properties, such as density and viscosity of the dried and water-saturated DESs, were measured. Finally, the removal of bisphenol A, a persistent micropollutant present in aqueous environments illustrates the potential of binary and ternary fatty acid-based DESs as extraction solvents. All prepared DESs showed good ability to extract bisphenol A from water with extraction efficiencies up to 92%.

MPI for Python provides bindings of the message passing interface (MPI) standard for the Python programming language and allows any Python program to exploit multiple processors.

A study of the conductance in a disordered linear chain of finite length L including inelastic scattering processes is presented. Inelastic scatterers are introduced as defined by B\"uttiker and are assumed to be uniformly distributed along the system. This defines an inelastic scattering time ${\mathrm{\ensuremath{\tau}}}_{\mathrm{in}}$ plus a condition of charge conservation which in turn introduces incoherent electrons. The four-probe conductance of the system is then reduced to a Landauer-like behavior G=2(${\mathit{e}}^{2}$/h)${\mathit{T}}_{\mathrm{eff}}$/ (1-${\mathit{T}}_{\mathrm{eff}}$), where the effective transmission through the sample, ${\mathit{T}}_{\mathrm{eff}}$, is the sum of two terms, one of which accounts for the phase-coherent electrons which have not suffered any inelastic collision and another for electrons which have suffered at least one inelastic collision in their journey. To show explicitly this point, the conductance of an ordered system is analyzed. Analytical and numerical results are presented for disordered chains, where resonances in the transmission present a width which is associated with the minimum between the escape time and the relaxation time. Because of the denominator in the Landauer formula, strong fluctuations on the conductance are present even in the weak-disordered situation in which the localization length \ensuremath{\lambda}>L, but we observed that they become of order ${\mathit{e}}^{2}$/h when the inelastic scattering length ${\mathit{L}}_{\mathrm{in}}$=L. Further decrease of the inelastic length causes the fluctuations to reduce following similar laws to that of the metallic regime.

Precise kinetic studies of photocatalytic reactions in solid catalyst water suspensions require the accurate description of the radiation fieldlight distributioninside the reactor. Solution of the radiative transport equation (RTE) inside the reaction is one of the best ways of accessing to such information. For solving this equation, a minimum of two parameters (the absorption and scattering coefficients) and one scattering spatial distribution function (the phase function) are needed. These attributes are directly associated with the optical behavior of the reacting system and are not independent of catalysts more conventional properties. A complete report on the physical and optical characteristics of titanium dioxide particulate suspensions in water is presented. Results were obtained for six different commercially available powders. The investigated parameters were (i) size of elementary particles, (ii) size of particle aggregates in water suspensions, (iii) specific surface area, (iv) spectral extinction coefficient, (v) spectral absorption coefficient, and (vi) spectral scattering coefficient. The last three were obtained as a function of wavelength in the range 275−405 nm. All measurements were made following a standardized protocol for the preparation of the solid suspensions. Scattering and absorption effects could be deconvoluted from the extinction coefficient by applying a very simple radiation transport model to the analysis of the experimental data. Experimental information was obtained by means of specially designed spectrophotometric measurements made with conventional cells, combined with results obtained with an integrating sphere accessory operated in the transmission mode. These propertiesparticularly the optical onesare required to solve the RTE and (i) to calculate precise values of photocatalytic reaction quantum yields and (ii) to fully characterize radiation energy absorption effects in the kinetics of photocatalytic reactions. Moreover, these data are indispensable for devising scaleup procedures in photocatalytic reactor design.

Abstract Tuning CO 2 hydrogenation selectivity to obtain targeted value‐added chemicals and fuels has attracted increasing attention. However, a fundamental understanding of the way to control the selectivity is still lacking, posing a challenge in catalyst design and development. Herein, we report our new discovery in ambient pressure CO 2 hydrogenation reaction where selectivity can be completely reversed by simply changing the crystal phases of TiO 2 support (anatase‐ or rutile‐TiO 2 ) or changing metal loadings on anatase‐TiO 2 . Operando spectroscopy and NAP‐XPS studies reveal that the determining factor is a different electron transfer from metal to the support, most probably as a result of the different extents of hydrogen spillover, which changes the adsorption and activation of the intermediate of CO. Based on this new finding, we can not only regulate CO 2 hydrogenation selectivity but also tune catalytic performance in other important reactions, thus opening up a door for efficient catalyst development by rational design.

Reducible oxides have been shown to greatly improve the activity of water gas shift (WGS) catalysts. The precise mechanism for this effect is a matter of intense debate, but the dissociation of water is generally considered to be the key step in the reaction. We present here a study of the water activation on oxygen vacancies at the support as part of the mechanism of the WGS reaction on Pt supported on pure and gallium-doped ceria. Doping the ceria with gallium allows tuning the vacancies in the support while maintaining constant the metal dispersion. An inverse relationship was found between the catalytic activity to WGS and the amount of oxygen vacancies. In situ time-resolved X-ray diffraction, mass spectrometry, and diffuse reflectance infrared spectroscopy (DRIFT) showed that the oxygen vacancy filling by water is always fast in either Pt/CeO2 or Pt/CeGa. DFT calculation provides molecular insights to understand the pathway of water reaction with vacancies at the metal–oxide interface sites. Our results suggest that the activation of the water molecule in the WGS mechanism is not the rate-limiting step in these systems. Concentration-modulation spectroscopy in DRIFT mode under WGS reaction conditions allows the selective detection of key reaction intermediates, a monodentate formate (HCOO) and carboxylate (CO2δ−) species, which suggests the prevalence of a carboxyl (HOCO) mechanism activated at the oxide–metal interface of the catalyst.

The flow induced by a long bubble steadily displacing a liquid confined by two closely located parallel plates or by a cylindrical tube of small diameter is numerically analyzed. The technique employed solves the complete set of governing equations simultaneously. The present analysis encompasses, and also extends, the whole range of Capillary values previously studied with various numerical techniques. The results shown uncover a type of recirculating flow pattern that appears to have been overlooked before. The effects of the inertial forces on the liquid flow rate are also assessed.

Current logistics and transportation (L&T) systems include heterogeneous fleets consisting of common internal combustion engine vehicles as well as other types of vehicles using “green” technologies, e.g., plug-in hybrid electric vehicles and electric vehicles (EVs). However, the incorporation of EVs in L&T activities also raise some additional challenges from the strategic, planning, and operational perspectives. For instance, smart cities are required to provide recharge stations for electric-based vehicles, meaning that investment decisions need to be made about the number, location, and capacity of these stations. Similarly, the limited driving-range capabilities of EVs, which are restricted by the amount of electricity stored in their batteries, impose non-trivial additional constraints when designing efficient distribution routes. Accordingly, this paper identifies and reviews several open research challenges related to the introduction of EVs in L&T activities, including: (a) environmental-related issues; and (b) strategic, planning and operational issues associated with “standard” EVs and with hydrogen-based EVs. The paper also analyzes how the introduction of EVs in L&T systems generates new variants of the well-known Vehicle Routing Problem, one of the most studied optimization problems in the L&T field, and proposes the use of metaheuristics and simheuristics as the most efficient way to deal with these complex optimization problems.

The adsorption of CO(2) over a set of gallium (III) oxide polymorphs with different crystallographic phases (alpha, beta, and gamma) and surface areas (12-105 m(2) g(-1)) was studied by in situ infrared spectroscopy. On the bare surface of the activated gallias (i.e., partially dehydroxylated under O(2) and D(2) (H(2)) at 723 K), several IR signals of the O-D (O-H) stretching mode were assigned to mono-, di- and tricoordinated OD (OH) groups bonded to gallium cations in tetrahedral and/or octahedral positions. After exposing the surface of the polymorphs to CO(2) at 323 K, a variety of (bi)carbonate species emerged. The more basic hydroxyl groups were able to react with CO(2), to yield two types of bicarbonate species: mono- (m-) and bidentate (b-) [nu(as)(CO(3)) = 1630 cm(-1); nu(s)(CO(3)) = 1431 or 1455 cm(-1) (for m- or b-); delta(OH) = 1225 cm(-1)]. Together with the bicarbonate groups, IR bands assigned to carboxylate [nu(as)(CO(2)) = 1750 cm(-1); nu(s)(CO(2)) = 1170 cm(-1)], bridge carbonate [nu(as)(CO(3)) = 1680 cm(-1); nu(s)(CO(3)) = 1280 cm(-1)], bidentate carbonate [nu(as)(CO(3)) = 1587 cm(-1); nu(s)(CO(3)) = 1325 cm(-1)], and polydentate carbonate [nu(as)(CO(3)) = 1460 cm(-1); nu(s)(CO(3)) = 1406 cm(-1)] species developed, up to approximately 600 Torr of CO(2). However, only the bi- and polydentate carbonate groups still remained on the surface upon outgassing the samples at 323 K. The total amount of adsorbed CO(2), measured by volumetric adsorption (323 K), was approximately 2.0 micromol m(-2) over any of the polymorphs, congruent with an integrated absorbance of (bi)carbonate species proportional to the surface area of the materials. Upon heating under flowing CO(2) (760 Torr), most of the (bi)carbonate species vanished a T > 550 K, but polydentate groups remained on the surface up to the highest temperature used (723 K). A thorough discussion of the more probable surface sites involved in the adsorption of CO(2) is made.

The availability of Roundup Ready (RR) varieties of soybean has increased the use of glyphosate for weed control in Argentina. Glyphosate [(N-phosphonomethyl)glycine] is employed for the eradication of previous crop vegetation and for weed control during the soybean growing cycle. Its action is effective, and low environmental impact has been reported so far. No residues have been observed in soil or water, either of glyphosate or its metabolite, AMPA (aminomethylphosphonic acid). The objective of this work was to monitor glyphosate and AMPA residues in soybean plants and grains in field crops in Santa Fe Province, Argentina. Five sites were monitored in 1997, 1998 and 1999. Individual soybean plants were sampled from emergence to harvest, dried and ground. Analysis consisted in residue extraction with organic solvents and buffers, agitation, centrifugation, clean-up and HPLC with UV detection. In soybean leaves and stems, glyphosate residues ranged from 1.9 to 4.4 mg kg(-1) and from 0.1 to 1.8 mg kg(-1) in grains. Higher concentrations were detected when glyphosate was sprayed several times during the crop cycle, and when treatments approached the flowering stage. AMPA residues were also detected in leaves and in grains, indicating metabolism of the herbicide.

The evaluation of the radiation field inside a slurry reactor constitutes a central step in the study of photocatalytic reactions. This task can be achieved by solving the radiative transfer equation (RTE) for the system under study. To solve the RTE, three optical properties of the catalyst suspensions are needed: the absorption coefficient, the scattering coefficient, and the phase function for scattering. In the present work, a novel experimental method to measure the optical properties of aqueous titanium dioxide (TiO2) suspensions is proposed. The method involved diffuse reflectance and transmittance spectrophotometric measurements of the catalyst suspensions, the evaluation of the radiation field in the sample cell, and the application of a nonlinear optimization program to adjust the model predictions to the experimental data. Three commercial brands of TiO2 were investigated: Aldrich, Degussa P25, and Hombikat UV 100.

Ceria (CeO2) has recently been found to be a promising catalyst in the selective hydrogenation of alkynes to alkenes. This reaction occurs primarily on highly dispersed metal catalysts, but rarely on oxide surfaces. The origin of the outstanding activity and selectivity observed on CeO2 remains unclear. In this work, we show that one key aspect of the hydrogenation reaction—the interaction of hydrogen with the oxide—depends strongly on the presence of O vacancies within CeO2. Through infrared reflection absorption spectroscopy on well-ordered CeO2(111) thin films and density functional theory (DFT) calculations, we show that the preferred heterolytic dissociation of molecular hydrogen on CeO2(111) requires H2 pressures in the mbar regime. Hydrogen depth profiling with nuclear reaction analysis indicates that H species stay on the surface of stoichiometric CeO2(111) films, whereas H incorporates as a volatile species into the volume of partially reduced CeO2–x(111) thin films (x ∼ 1.8–1.9). Complementary DFT calculations demonstrate that oxygen vacancies facilitate H incorporation below the surface and that they are the key to the stabilization of hydridic H species in the volume of reduced ceria.

The design of paper-based assays that integrate passive pumping requires a precise programming of the fluid transport, which has to be encoded in the geometrical shape of the substrate. This requirement becomes critical in multiple-step processes, where fluid handling must be accurate and reproducible for each operation. The present work theoretically investigates the capillary imbibition in paper-like substrates to better understand fluid transport in terms of the macroscopic geometry of the flow domain. A fluid dynamic model was derived for homogeneous porous substrates with arbitrary cross-sectional shapes, which allows one to determine the cross-sectional profile required for a prescribed fluid velocity or mass transport rate. An extension of the model to slit microchannels is also demonstrated. Calculations were validated by experiments with prototypes fabricated in our lab. The proposed method constitutes a valuable tool for the rational design of paper-based assays.

Skin penetration of active molecules for treatment of diverse diseases is a major field of research owing to the advantages associated with the skin like easy accessibility, reduced systemic-derived side effects, and increased therapeutic efficacy. Despite these advantages, dermal drug delivery is generally challenging due to the low skin permeability of therapeutics. Although various methods have been developed to improve skin penetration and permeation of therapeutics, they are usually aggressive and could lead to irreversible damage to the stratum corneum. Nanosized carrier systems represent an alternative approach for current technologies, with minimal damage to the natural barrier function of skin. In this Review, the use of nanoparticles to deliver drug molecules, genetic material, and vaccines into the skin is discussed. In addition, nanotoxicology studies and the recent clinical development of nanoparticles are highlighted to shed light on their potential to undergo market translation.

The long‐term planning of the shale gas supply chain is a relevant problem that has not been addressed before in the literature. This article presents a mixed‐integer nonlinear programming (MINLP) model to optimally determine the number of wells to drill at every location, the size of gas processing plants, the section and length of pipelines for gathering raw gas and delivering processed gas and by‐products, the power of gas compressors, and the amount of freshwater required from reservoirs for drilling and hydraulic fracturing so as to maximize the net present value of the project. Because the proposed model is a large‐scale nonconvex MINLP, we develop a decomposition approach based on successively refining a piecewise linear approximation of the objective function. Results on realistic instances show the importance of heavier hydrocarbons to the economics of the project, as well as the optimal usage of the infrastructure by properly planning the drilling strategy. © 2014 American Institute of Chemical Engineers AIChE J , 60: 2122–2142, 2014

In this work the interfacial shapes and the flow occurring at the trailing meniscus of a long bubble is numerically analyzed. The technique employed solves the complete set of governing equations simultaneously. The numerical results reported complete previous descriptions of the creeping flow regime; the influence of the inertia forces on the free surface shapes, interfacial undulations, and flow patterns is also analyzed.

An important industrial problem is the short-term scheduling of batch multiproduct facilities where a wide range of products are manufactured in small amounts that must be satisfied at certain due dates during the given time horizon. This paper presents a new MILP mathematical formulation for the batch scheduling problem involving a single processing stage for every product to be delivered. Based on a continuous representation of the time domain and the concept of job predecessor and successor to effectively handle changeovers, the proposed model is able to determine the optimal allocation of jobs to lines/units, the sequence of jobs on every line/unit, and their starting and completion times so as to minimize one of the following problem objectives: the overall tardiness, the schedule makespan, or the number of tardy orders. Facilities having nonidentical parallel units/lines, sequence-dependent changeovers, finite release times for units and orders, and restrictions on the types of orders that can be manufactured in each equipment can easily be handled. To deal with real world single-stage scheduling problems, a successful strategy for expediting the problem solution that relies on the use of heuristics is also reported. These heuristics allow one to partially prune the set of feasible predecessors for each customer order, reducing the size of the MILP problem representation. Examples involving up to 20 orders and 4 units were successfully solved with an advanced branch-and-bound code requiring reasonable CPU time.

We report a study of the epoxidation of soybean oil and soybean methyl esters with hydrogen peroxide in dilute solution (6 wt%) using an amorphous heterogeneous Ti/SiO2 catalyst in the presence of tert-butyl alcohol. The influence of some relevant process variables such as temperature and the hydrogen peroxide-to-double bond molar ratio on performance is examined. The highest yields of epoxidized olefins were obtained upon using a H2O2 ∶ substrate molar ratio of 1.1 ∶ 1. Higher ratios than this were not effective for speeding up the reaction. Under the experimental conditions employed in this work, no degradation of the oxirane ring was observed.

The electronic structure and frequency dependent dielectric function $\ensuremath{\varepsilon}(\ensuremath{\omega})$ of rocksalt semiconductors PbSe and PbTe are investigated using the local density approximation (LDA) and the generalized gradient approximation as two different exchange and correlation approximations, within the full-potential linearized augmented plane-wave approach. Spin-orbit coupling has been incorporated in the study. The results are presented and compared with other recent calculations and experimental data. Structural properties are also obtained by means of calculations of total energy as a function of lattice parameters. The bulk structural parameters are sensitive to the choice of exchange and correlation approximation. The essential features of the band structure and density of states of PbSe and PbTe are reproduced by our calculations and agree quite well with available experimental results. The position of the minimum energy gap is correctly predicted, although the value of the gap is as usual, underestimated by the local density approximation with respect to the experimental data. This gap value is improved by the inclusion of the generalized gradient approximation. Also, we have calculated the real $[{\ensuremath{\varepsilon}}_{1}(\ensuremath{\omega})]$ and imaginary $[{\ensuremath{\varepsilon}}_{2}(\ensuremath{\omega})]$ parts of $\ensuremath{\varepsilon}(\ensuremath{\omega})$ for both compounds, in the framework of the LDA scheme for exchange and correlation. The inclusion of spin-orbit coupling leads to a richer structure in both ${\ensuremath{\varepsilon}}_{1}(\ensuremath{\omega})$ and ${\ensuremath{\varepsilon}}_{2}(\ensuremath{\omega}).$ The agreement with experimental results is satisfactory.