Role of Van der Waals forces in graphene adsorption over: Pd, Pt, Ni

We report ab initio computations with the Vienna Ab initio Simulation Package (VASP) aimed at elucidating the adsorption mechanism of graphene-like structures on (111) Pd, Pt, and Ni surfaces. To study the adsorption properties, we simulate an already-formed graphene layer. We present a comparative discussion of the graphene interactions with the three metals, focusing on the very particular adsorption of graphene over PdFil: Quiroga, María Alejandra. Universidad Nacional del Sur. Departamento de Fisica; Consejo Nacional de Invest Cientifícas y Tecnicas. Centro Cientifico Tecnológico - Conicet - Bahia Blanca. Instituto de Fisica del Sur; Argentina;Fil: Cabeza, Gabriela Fernanda. Consejo Nacional de Invest Cientifícas y Tecnicas. Centro Cientifico Tecnológico - Conicet - Bahia Blanca. Instituto de Fisica del Sur; Argentina; Universidad Nacional del Sur. Departamento de Fisica

Thermodynamic properties of Pt nanoclusters: an ab initio study

Nanoparticles (NPs) and subnanometer clusters exhibit novel physical andchemical properties that differ significantly from their counterpart bulkmaterials.  This is mainly originatedfrom the large fraction of subordinated atoms at the surface for NP of small sizes.Concerning thermodynamic properties, in spite of the fact that a large amountof research has been performed, there are still fundamental questions not yetresolved since in general the conventional thermodynamic knowledge of macroscopic metals does notapply for these nanoscopic systems. As thesize of the NPs is reduced, anomalous behaviors have been reported in theirthermodynamic properties, such as deviations from the Debye law of the specificheat and negative thermal expansion [[1],[2]].The Debyetemperature is a fundamental property, since it is closely related to changesin the vibrational properties and specific heat. For Pt NPs capped with PVP-k30the Debye temperature (QD) wasmeasured by the extended X-ray absorption finestructure (EXAFS) technique leading to values higher than for the bulk [[3]].On the other side for small subnanometer Pt NPs (of approximately 0.9  ± 0.2 nm and Navg ~16 atoms) supported on Al2O3 experimental studies based on scanning transmissionelectron microscopic (STEM) and X-ray absorptionspectroscopy exhibit marked contractions of thePt-Pt bond distances with respect to bulk values, and a negative thermalexpansion of these interatomic distances [[4]].In principle, in both works, the surface atom contraction and the interactionof the Pt atoms with capping molecules or support, both enhanced because of thenanosized dimensions of the NP, were indicated as possible reasons to explainthese anomalous thermodynamic properties. Motivatedby these experimental findings, and, as a first step to investigate theseproblems, in this work we calculate the thermodynamic properties of isolated PtNPs for sizes between 13-55 atoms. By considering isolated NPs, we expect toshed some light on the problem by considering only the intrinsic effects of thesmall dimension of NPs. We first determine their equilibrium geometries, tofurther evaluate their vibrational density of states (VDOS), the specific heatand the Debye temperature. The explicit thermal evolution of the averageinteratomic distances is determined at various temperatures by developing abinitio molecular dynamics. We find that the relaxed interatomic distances arereduced with respect to the bulk ones, in agreement with the experiments. The VDOSare very different from the bulk ones, with the presence of discrete states,which give rise to deviations from the typical Debye model of the specific heatat constant volume and low temperatures. Estimations of the Debye temperatureindicate values lower that those calculated for the solid.Fil: Maldonado, Abel Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería; ArgentinaFil: Cabeza, Gabriela Fernanda. Universidad Nacional del Sur. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Ramos, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería; ArgentinaSimposio Latinoamericano de Física del Estado Sólido XXIIISan Carlos de BarilocheArgentinaCentro Atómico BarilocheInstituto Balseir

Usefulness of Sōna Aspergillus Galactomannan LFA with digital readout as diagnostic and as screening tool of COVID-19 associated pulmonary aspergillosis in critically ill patients. Data from a multicenter prospective study performed in Argentina

COVID-19-associated pulmonary aspergillosis (CAPA) incidence varies depending on the country. Serum galactomannan quantification is a promising diagnostic tool since samples are easy to obtain with low biosafety issues. A multicenter prospective study was performed to evaluate the CAPA incidence in Argentina and to assess the performance of the lateral flow assay with digital readout (Sōna Aspergillus LFA) as a CAPA diagnostic and screening tool. The correlation between the values obtained with Sōna Aspergillus LFA and Platelia® EIA was evaluated. In total, 578 serum samples were obtained from 185 critically ill COVID patients. CAPA screening was done weekly starting from the first week of ICU stay. Probable CAPA incidence in critically ill patients was 10.27% (19/185 patients when LFA was used as mycological criteria) and 9% (9/100 patients when EIA was used as mycological criteria). We found a very good correlation between the two evaluated galactomannan quantification methods (overall agreement of 92.16% with a Kappa statistic value of 0.721). CAPA diagnosis (>0.5 readouts in LFA) were done during the first week of ICU stay in 94.7% of the probable CAPA patients. The overall mortality was 36.21%. CAPA patients' mortality and length of ICU stay were not statistically different from for COVID (non-CAPA) patients (42.11 vs 33.13% and 29 vs 24 days, respectively). These indicators were lower than in other reports. LFA-IMMY with digital readout is a reliable tool for early diagnosis of CAPA using serum samples in critically ill COVID patients. It has a good agreement with Platelia® EIA. Lay Summary: The incidence of COVID-associated pulmonary aspergillosis (CAPA) in critically-ill Argentinian patients was established (10.27%). Serum galactomannan quantification was useful as a screening tool for this mycosis. A good agreement between Platelia® EIA and Sōna Aspergillus LFA is reported.Fil: Giusiano, Gustavo Emilio. Universidad Nacional del Nordeste. Instituto de Medicina Regional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; ArgentinaFil: Fernández, Norma Beatriz. Universidad de Buenos Aires. Facultad de Medicina. Hospital de Clínicas General San Martín; ArgentinaFil: Vitale, Roxana Gabriela. Gobierno de la Ciudad de Buenos Aires. Hospital General de Agudos "Ramos Mejía"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alvarez, Christian. No especifíca;Fil: Ochiuzzi, María Eugenia. Gobierno de la Ciudad Autonoma de Buenos Aires. Hospital General de Agudos Carlos Durand.; ArgentinaFil: Santiso, Gabriela Maria. Gobierno de la Ciudad de Buenos Aires. Hospital de Infecciosas "Dr. Francisco Javier Muñiz"; ArgentinaFil: Cabeza, Matías Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; ArgentinaFil: Tracogna, Fernanda. Gobierno de la Provincia de Chaco. Hospital Julio Cecilio Perrando.; ArgentinaFil: Farias L. Hospital de Clínicas José de San Martín Universidad; ArgentinaFil: Afeltra, Javier. Gobierno de la Ciudad de Buenos Aires. Hospital Gral.de Agudos "ramos Mejia". Departamento de Diagnostico y Tratamiento; ArgentinaFil: Noblega, Luciana María. No especifíca;Fil: Giuliano, Carla Valeria. Gobierno de la Ciudad Autonoma de Buenos Aires. Hospital General de Agudos Carlos Durand.; ArgentinaFil: Garcia, Guillermo Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; Argentin

Correlation between magnetic and crystal structural sublattices in palladium-doped FeRh alloys: Analysis of the metamagnetic phase transition driving forces

FeRh alloys doped with the third element exhibit a change in the lattice and magnetic subsystems, which are manifested in antiferromagnetic- ferromagnetic (AFM-FM) first-order phase transition temperature, the shrinkage of the temperate hysteresis under transition, and the reduction of the saturation magnetization. All aforementioned parameters are crucial for practical applications. To control them it is quite important to determine the driving forces of the metamagnetic transition and its origins. In this manuscript ab initio calculations and experimental studies results are presented, which demonstrate the correlation between the structural and magnetic properties of the Fe50Rh50−xPdx alloys. The qualitative analysis of the metamagnetic phase transition driving forces in palladium-doped FeRh alloys was performed to determine their contribution to the evolution of magnetic and lattice subsystems. In addition, the impact of the impurities phases together with its magnetic behavior on the AFM-FM phase transition was considered.Fil: Komlev, Aleksei S.. Lomonosov Moscow State University; RusiaFil: Karpenkov, Dmitriy Y.. National University of Science and Technology; Rusia. Lomonosov Moscow State University; RusiaFil: Gimaev, Radel R.. Lomonosov Moscow State University; RusiaFil: Chirkova, Alisa. Institute for Materials Science; AlemaniaFil: Akiyama, Ayaka. Hirosaki University; JapónFil: Miyanaga, Takafumi. Hirosaki University; JapónFil: Hupalo, Marcio Ferreira. Universidade Estadual do Ponta Grossa; BrasilFil: Aguiar, D.J.M.. Universidade Federal do Paraná; BrasilFil: Carvalho, Alexandre Magnus G.. Universidade Estadual de Maringá; Brasil. Universidade Federal de Sao Paulo; BrasilFil: Jiménez, María Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Zverev, Vladimir I.. Lomonosov Moscow State University; RusiaFil: Perov, Nikolai S.. Lomonosov Moscow State University; Rusi

Electronic and magnetic properties of Pd-Ni multilayers: Study using density functional theory

Electronic and magnetic properties of Pd-Ni multilayers have been studied using VASP method in the framework of the density functional theory (DFT). The calculations performed for different configurations (Pd n/Ni m(1 1 1), where n Pd layers are piled up over m Ni layers with n=0 to 4 and n+m=4), reveal that the important magnetic moment of Ni is significantly enhanced according as n increases due to hybridization effects between Pd and Ni mostly localized at the interface. The results also indicate that the Pd atoms are strongly polarized in the studied systems when compared with the pure metalFil: Gómez, Guillermina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Belelli, Patricia Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin

Growth of carbon structured over Pd, Pt and Ni: a comparative DFT study

To elucidate the graphene-like structures mechanisms growth over the M(1 1 1) surface (M = Pd, Pt and Ni) we performed ab initio calculus in the frame of density functional theory with the exchange-correlation functional treated according to the Generalized Gradient Approximation (GGA). In order to avoid the problem that representthe complex interaction between the well formed graphene layer and the metallic surface, we recreate the carbon rings formation initial steps, by adding one by one carbon atoms over M(1 1 1) surface. With this strategy, the chemical bonding is always present until the graphene layer is wellformed, in which case the GGAneglects van derWaals dispersive forces.We investigate the electronic properties by studying the band structure and the density of states.Fil: Quiroga, Matías Abel Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin

Theoretical study on the electronic and catalytic properties of Fe-doped TiO2 and its use in the removal of arsenic

Arsenic (As) is atoxic element that can be fatal to humans. In the environment, it exists indifferent oxidation states (-III, 0, + III and + V). However, in natural water,the As is mainly found in inorganic form forming as oxyanions of trivalentarsenite As (III) or pentavalent arsenate As (V) depending on the redoxpotential and the pH of the water. The contamination of water with arsenic is aglobal problem related mainly to its extensive presence in water resources usedfor human consumption1. Arsenate is more stable, less mobile andtoxic than As (III) and more efficiently removed from water. Therefore, commonmethods for the removal of arsenic from water involve the oxidation of the As(III) to As (V) species. As an alternative to conventional procedures,different proposals have attracted considerable attention in recent years,including heterogeneous photocatalysis with titanium dioxide (TiO2)and the use of zero valent iron (Fe0) known as ZVI. At present, two experimental studies can be mentioned,a recent one by López-Muñoz2 and another study by Nguyen et al. informing the use ofphotocatalysis with TiO2and ZVI nanoparticles (NP-ZVI) for the removal of As (III) from aqueous systems3.The results obtained demonstrated an increase in the arsenic removal efficiencyof the aqueous solution when ZVI particles were added to the reactor. As photocatalysis with both systems pure TiO2and in combination with iron offer attractive advantages for the treatment ofarsenic in aqueous systems, it is interesting to compare their performance andexplore the potential synergism between them. That is why in this work bothsystems were modeled with the objective of determining the mainphysical-chemical parameters that control the activity and selectivity towardsthe oxidation of arsenic (As). The calculations were made using the VASP4code within the formalism of the Functional Density theory, with the inclusionof the Hubbard coefficient (DFT + U). The chosen surfaces of the titania are thecatalytically most active, anatase TiO2(101) and rutile TiO2(110). The As/TiO2 interaction was modeled by depositing 1, 2 or 4As0 atoms. Different Fe-doping options (cationic and interstitial)were studied. The As adsorption energies were calculated on both surfaces. The study is completed with the analysis of the adsorption of different arsenious species.Fil: Morgade, Cecilia Ines Nora. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaVI San Luis School and Conference on Surfaces, Interfaces and CatalysisSanta FeArgentinaConsejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fé. Instituto de Investigaciones en Catálisis y PetroquímicaUniversidad Nacional del Litora

First-principles study of codoping TiO2 systems capable of improving the specific surface area and the dissociation of H2O to generate H2 and O2

In this study, theoretical results of structural, electronic and magnetic properties of codoped anatase TiO2 using metals (Pt, V) and nonmetals (C, N) to obtain insight into the codoping effect are reported. Results of monodoped systems with N, C, V and Pt are also reported. The way different pairs of metal-nonmetal dopants affect the positions of the edge of the valence and conduction bands, and consequently their redox potential in the search for the best candidate for water splitting into H2 and O2 has also been studied. In this sense, density functional calculations show that the particular case of Pt-C@Ti codoped TiO2 would be the most efficient for the mentioned reaction. In addition, it is pointed out that the formation of particular structures observed is due to the interaction metal-nonmetal (M-NM) rather than the particular nature of the foreign atoms. The analysis also shows that the systems presenting the highest interplanar spacing in the crystal structure are V-C@O and Pt-C@O, unlike Pt-N@O that has not shown significant modifications. This could translate into an enhancement in the specific surface area, particularly observed in the case of [email protected]: Morgade, Cecilia Ines Nora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin

Synergetic interplay between metal (Pt) and nonmetal (C) species in codoped TiO2: A DFT+U study

The structural, energetic, magnetic and electronic properties of Pt-C-doped and Pt/C-codoped TiO2 have been studied using first-principle calculations to elucidate the effect of the metal-nonmetal interactions. Compared with other non-metals, C-doping induces the formation of complex structures on titania. From the analysis of the electronic structures of the C-doping system, band gap narrowing as well as the formation of localized gap states are observed in it. The calculated results are in agreement with the experimental absorptions observed in the UV-visible diffuse reflectance spectroscopy spectra. Based on our results, the main findings relating to Pt/C codoping are the formation of highly symmetric coordination-like compounds and the formation of impurity states in the band gap that could be propitious for the separation of photoexcited electron-hole pairs. Is especially remarkable the case of Pt/C@Ti-codoped TiO2 which could be the most effective for the redox reaction of H2O to produce H2 and O2 because it presents the greatest narrowing of the band gap, the lower shift of the conduction band and it is the only one that favorably modifies the position of valence band. All are necessary conditions for the reaction mentioned.Fil: Morgade, Cecilia Ines Nora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Tecnológica Nacional; ArgentinaFil: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin