Luiz Frederico Rodrigues | Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS) (original) (raw)

Papers by Luiz Frederico Rodrigues

Spectrochimica Acta Part B: Atomic Spectroscopy, 2011

The trace impurities Cr, Cu, Fe, K, Mn, Sb and Zn were determined in powdered aluminum nitride by... more The trace impurities Cr, Cu, Fe, K, Mn, Sb and Zn were determined in powdered aluminum nitride by direct solid sampling graphite furnace atomic absorption spectrometry using a ZEEnit 60 atomic absorption spectrometer. This spectrometer features inverse Zeeman-effect background correction and a variable magnetic field enabling measurements in two sensitivity modes over a concentration range of three orders of magnitude.

Neste trabalho foram determinadas baixas concentracoes de Cd, Cu e Pb em catalisadores a base de ... more Neste trabalho foram determinadas baixas concentracoes de Cd, Cu e Pb em catalisadores a base de alumina, por espectrometria de absorcao atomica com forno de grafite, com amostragem direta de solidos (DSS-GF AAS). Os catalisadores analisados sao utilizados extensamente na industria petroquimica. As concentracoes dos constituintes majoritarios foram determinadas por ICP OES com o objetivo de caracterizar a matriz. Os seguintes parâmetros analiticos foram avaliados: temperaturas de pirolise e atomizacao, a praticidade da calibracao com solucoes de referencia, a necessidade do uso de paladio como modificador e a influencia da quantidade de massa introduzida no atomizador. Amostras entre 0,05 a 30 mg foram usadas e paladio foi considerado desnecessario para todos os elementos. Os resultados foram comparados com aqueles obtidos por espectrometria de emissao optica com plasma indutivamente acoplado (ICP OES), por espectrometria de massa com plasma indutivamente acoplado (ICP-MS) e por esp...

Diisocianato de difenilmetano polimerico (PMDI) e difenilmetano dianilina (MDA) sao importantes m... more Diisocianato de difenilmetano polimerico (PMDI) e difenilmetano dianilina (MDA) sao importantes materia-primas na industria de poliuretanos. Esses produtos tem uma ampla aplicacao em diversas areas como a medicina, catalise e eletronica. Atualmente, um consideravel interesse tem sido dado em relacao a presenca de contaminantes metalicos em materias-primas para a producao de polimeros, pois estes influenciam no processamento e alteram as propriedades termicas dos produtos. Desta forma, neste trabalho e proposto um procedimento para a determinacao de Cr, Fe, Mg, Mn, Na e Ni utilizando a amostragem direta por espectrometria de absorcao atomica com forno de grafite (DS-GF AAS). Inicialmente, obtiveram-se as curvas de pirolise e atomizacao para as amostras de PMDI, MDA e solucoes de referencia. Foi possivel a quantificacao dos analitos empregando a calibracao com o uso de solucoes de referencia aquosas. Alem disso, utilizou-se o recurso do corretor por efeito Zeeman com campo magnetico v...

Journal of the Brazilian Chemical Society, 2017

This work performs an exploratory analysis of the sparkling wines from the state of Rio Grande do... more This work performs an exploratory analysis of the sparkling wines from the state of Rio Grande do Sul, Brazil. Samples of traditional sparkling wine and Moscatel sparkling wine were analyzed and chemometrics tools were applied to physicochemical, gas chromatography and stable carbon isotope analysis. The carbon isotope ratio (δ 13 C-CO 2) of the samples presents great heterogeneity and confirm that the isotopic signature of the CO 2 could be derived from the fermentation of C4 sugar. The principal component analysis (PCA) was capable to discriminate and classify the samples in their respective groups and combined data approach was especially important to identify the correlation between the studied variables. With the increasing production of sparkling wines in Brazil, this work helps to evaluate the standards of the local sparkling wines.

Materials Research, 2019

This study evaluates the properties of chitosan (CS) membranes modified with different percentage... more This study evaluates the properties of chitosan (CS) membranes modified with different percentages (0.5%, 3%, and 5% w/w) of a graphene-based material. Graphene oxide (GO) and reduced graphene oxide (RGO) were obtained by the chemical exfoliation of graphite and thermal reduction. Then, they were characterized by electrical conductivity measurements, FESEM, XRD, AFM, and Raman spectroscopy. The composites' morphology was evaluated by FESEM. The degree of swelling over a 48 h period and mass loss behavior in phosphate-buffered saline solution for up to 70 days were also studied. The hydrophilicity of the CS and CS/graphene nanocomposites was examined by water contact angle. The graphene materials showed small stacks (6-8 sheets) with low defect density and nanoscale thickness (1.3-5.9 nm). The dispersion of the graphene material in the CS matrix significantly decreased the degree of swelling (460%) but did not modify the hydrolytic degradation process and the hydrophilicity of membranes.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2015

Nature Communications, 2020

Ocean warming related to climate change has been proposed to cause the dissociation of gas hydrat... more Ocean warming related to climate change has been proposed to cause the dissociation of gas hydrate deposits and methane leakage on the seafloor. This process occurs in places where the edge of the gas hydrate stability zone in sediments meets the overlying warmer oceans in upper slope settings. Here we present new evidence based on the analysis of a large multi-disciplinary and multi-scale dataset from such a location in the western South Atlantic, which records massive gas release to the ocean. The results provide a unique opportunity to examine ocean-hydrate interactions over millennial and decadal scales, and the first evidence from the southern hemisphere for the effects of contemporary ocean warming on gas hydrate stability. Widespread hydrate dissociation results in a highly focused advective methane flux that is not fully accessible to anaerobic oxidation, challenging the assumption that it is mostly consumed by sulfate reduction before reaching the seafloor.

Marine and Petroleum Geology, 2015

The Rio Grande Cone is a large-scale fanlike feature in the continental slope of the Pelotas Basi... more The Rio Grande Cone is a large-scale fanlike feature in the continental slope of the Pelotas Basin, Southern Brazil, where ubiquitous world-class bottom simulating reflectors (BSRs) are readily observed in seismic records. With the purpose of searching for natural gas hydrate deposits in the Cone area, four oceanographic cruises were carried out between May 2011 and July 2013, leading to the discovery of two pockmark fields, active faults and gas hydrates in shallow sediments. Multichannel seismic, multibeam echo sounder, side scan sonar and sub-bottom profiler records were used to map the shallow section and select sites for piston core sampling. Gas hydrates were recovered in several piston cores within muddy sediments collected inside pockmarks displaying high backscatter in the multibeam and side scan sonar data. We present two representative piston cores where numerous levels of gas hydrates occur, along with degassing features, authigenic carbonate and soupy sediments. Gas dissociated from gas hydrate samples is dominantly methane (> 99.78 %) with minor quantities of ethane. The chemical and isotopic compositions of the gas strongly suggest a biogenic origin for the

Advances in Natural and Technological Hazards Research, 2013

The central Nile Deep-Sea Fan contains a broad area of seabed destabilisation in association with... more The central Nile Deep-Sea Fan contains a broad area of seabed destabilisation in association with fluid seepage: slope-parallel sediment undulations are associated with multibeam high-backscatter patches (HBPs) related to authigenic carbonates. During the 2011 APINIL campaign, a deep-towed sidescan and profiling system (SAR) was used to acquire high-resolution data along three transects across water depths of 1,700-2,650 m. Three seabed domains are distinguished, all developed within stratified sediments overlying mass-transport deposits (MTDs). Upslope of the undulations (<1,950 m), sidescan HBPs record focused fluid seepage via seabed cracks. In the western area of undulations, sidescan HBPs are distinct from intermediate-backscatter patches (IBPs) that extend up to 850 m parallel to the undulations, mainly along their downslope flanks; some contain sub-circular HBPs up to 300 m wide, three associated with smaller (<10 m) hydroacoustic gas flares. Focused fluid seeps are inferred to have shifted over time to form elongate carbonate pavements, preferentially along the footwalls of faults beneath the undulations that provide pathways for fluid flow. In contrast, in the eastern area of undulations, sidescan imagery reveal only slope-transverse furrows formed by turbulent flows, interpreted to indicate that fossil carbonates sampled during submersible operations have been exhumed by erosion.

Journal of Chemical Engineering & Process Technology, 2014

realizada por espectrometria de absorção atômica com atomização eletrotérmica e amostragem direta... more realizada por espectrometria de absorção atômica com atomização eletrotérmica e amostragem direta de sólidos (DSS-ET AAS, corretor de fundo com fonte de deutério). Foram avaliados os parâmetros de aquecimento, uso de Pd como modificador químico, possibilidade de calibração com soluções aquosas e massa máxima de amostra. Para comparação dos resultados as amostras foram analisadas por espectrometria de massa com plasma indutivamente acoplado (ICP-MS) e espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES) após decomposição por via úmida em sistema de alta pressão assistida por micro-ondas e também por combustão iniciada por micro-ondas. Não foram observadas diferenças significativas entre os resultados obtidos pelo método proposto e pelas outras técnicas. A exatidão também foi avaliada por comparação com resultados de análise por ativação neutrônica (NAA). A calibração foi possível com soluções de referência aquosas. Os sinais de fundo foram sempre inferiores a ...

Gas hydrate provinces are present in at least in two areas along Brazil’s continental margi... more Gas hydrate provinces are present in at least in two areas along Brazil’s continental margin: (1) the Rio Grande Cone in the southeast, and (2) the Amazon deep-sea fan in the equatorial region. The occurrence of gas hydrates in these depocentres was first detected geophysically and has recently been proven by seafloor sampling of gas vents, detected as water column acoustic anomalies rising from seafloor depressions (pockmarks) and/or mounds, many associated with seafloor faults. The gas vents include typical features of cold seep systems, including shallow sulphate reduction depths (<4 m), authigenic carbonate pavements and chemosynthetic ecosystems. In both areas, gas sampled in hydrate and in sediments is dominantly formed by biogenic methane. Calculation of the methane hydrate stability zone for water temperatures in the two areas shows that gas vents occur along its feather edge (water depths between 510-760 m in the Rio Grande Cone and 500-670 m in the Amazon deep-sea...

Radiocarbon

ABSTRACTThe Rio Grande Cone is a major fanlike depositional feature in the continental slope of t... more ABSTRACTThe Rio Grande Cone is a major fanlike depositional feature in the continental slope of the Pelotas Basin, Southern Brazil. Two representative sediment cores collected in the Cone area were retrieved using a piston core device. In this work, the organic matter (OM) in the sediments was characterized for a continental vs. marine origin using chemical proxies to help constrain the origin of gas in hydrates. The main contribution of OM was from marine organic carbon based on the stable carbon isotope (δ13C-org) and total organic carbon/total nitrogen ratio (TOC:TN) analyses. In addition, the 14C data showed important information about the origin of the OM and we suggest some factors that could modify the original organic matter and therefore mask the “real” 14C ages: (1) biological activity that could modify the carbon isotopic composition of bulk terrestrial organic matter values, (2) the existence of younger sediments from mass wasting deposits unconformably overlying older s...

Geo-Marine Letters

Deep-sea fans have been proposed to act as carbon sinks, rapid deposition driving shallow methano... more Deep-sea fans have been proposed to act as carbon sinks, rapid deposition driving shallow methanogenesis to favor net storage within the gas hydrate stability zone (GHSZ). Here, we present new evidence of widespread gas venting from the GHSZ on the upper Amazon deep-sea fan, together with analyses of the first samples of gas hydrates recovered offshore NE Brazil. Multibeam water column and seafloor imagery over an 18,000-km 2 area of the upper Amazon fan reveal 53 water column gas plumes, rising from venting features in water depths of 650-2600 m. Most gas vents (60%) are located along seafloor faults that record the ongoing gravitational collapse of the fan above deep décollements, while others (40%) are located in water depths of 650-715 m within the upper edge of the GHSZ. Gas compositions from hydrates recovered in vents at three locations on and north of the fan indicate biogenic sources (dominantly methane with 2-15% of CO 2 ; δ 13 C from − 81.1 to − 77.3‰), whereas samples from vents adjacent to the fan proper include possible thermogenic contributions (methane 95%, CO 2 4%, and ethane 1%; δ 13 C-59.2‰). These results concur with previous findings that the upper edge of the GHSZ may be sensitive to temporal changes in water temperatures, but further point to the importance of gas escape from within areas of gas hydrate stability. Our results suggest the role of fluid migration along pathways created by faulting within rapidly deposited passive margin depocenters, which are increasingly recognized to undergo gravitational collapse above décollements. Our findings add to evidence that gas can escape from sediments to the sea in areas where gas hydrates are stable on passive margins, and suggest the need of further studies of the dynamics of deep-sea depocenters in relation to carbon cycling.

Environmental monitoring and assessment, Jan 6, 2018

The present work evaluates the efficiency of some low-cost sampler container for a reliable carbo... more The present work evaluates the efficiency of some low-cost sampler container for a reliable carbon stable isotope analysis of methane. The procedure efficiency was evaluated for five containers, through 91 days, under two storage temperatures (4 °C and 25 °C) and the results are compared against a reference sampler by using univariate and multivariate statistical methods. Based on the univariate (ANOVA and comparison statistical methods) and multivariate (PCA and HCA) statistical methods, it was identified that (i) the isotopic value changes with time and, in this way, must be taken in account when choosing the appropriate sampler and (ii) the lower temperature reduces the isotopic fractionation process and is preferable for the gas sample storage. Among the storage systems, two options were found to be statistically equivalent to the reference container (IsoJar) for a time horizon of 91 days. We found that the exetainer (4 °C and 25 °C) storage systems are statistically equivalent ...

Waste management (New York, N.Y.), Jan 16, 2018

Leachate produced during an organic matter decomposition process has a complex composition and ca... more Leachate produced during an organic matter decomposition process has a complex composition and can cause contamination of surface and groundwaters adjacent to a landfill area. The monitoring of these areas is extremely important for the characterization of the leachate produced and to avoid or mitigate environmental damages. Thus, the present study has the objective of monitoring the area of a Brazilian landfill using conventional parameters (dissolved metals and anions in water) and alternative, stable carbon isotopes parameters (δC of dissolved organic and inorganic carbons in water) in addition to multivariate analysis techniques. The use of conventional and alternative parameters together with multivariate analysis showed that cells of the residues are at different phases of stabilization of the organic matter and probably already at C3 of the methanogenic phase of decomposition. In addition, the data showed that organic matter stabilization ponds present in the landfill are eff...

Environmental science and pollution research international, Jan 25, 2017

In Brazil, landfills are commonly used as a method for the final disposal of waste that is compli... more In Brazil, landfills are commonly used as a method for the final disposal of waste that is compliant with the legislation. This technique, however, presents a risk to surface water and groundwater resources, owing to the leakage of metals, anions, and organic compounds. The geochemical monitoring of water resources is therefore extremely important, since the leachate can compromise the quality and use of surface water and groundwater close to landfills. In this paper, the results of analyses of metals, anions, ammonia, and physicochemical parameters were used to identify possible contamination of surface water and groundwater in a landfill area. A statistical multivariate approach was used. The values found for alkali metals, nitrate, and chloride indicate contamination in the regional groundwater and, moreover, surface waters also show variation when compared to the other background points, mainly for ammonia. Thus, the results of this study evidence the landfill leachate influence...