249 research outputs found
Understanding the Influence of the Biomass-Derived Alcohols on the Activity and Stability of Pt Nanoparticles Supported on Graphene Nanoribbons
We produced Pt/GNRs by a one-step synthesis procedure and evaluated their electroactivity and stability towards glycerol electrooxidation reaction (GEOR) for the first time. We compared the electrocatalytic performance of GEOR with methanol and ethanol electrooxidation on Pt/GNRs at identical experimental conditions. The activities and stabilities for the electrooxidation of these biomass-derived alcohols on Pt/GNRs were compared to commercial Pt/C. The synthesis of the Pt/GNRs was confirmed by transmission electron microscopy, x-ray diffractometry, ultraviolet spectrophotometry, and Raman spectroscopy. We found that the activities of Pt/GNRs for these reactions are comparable to Pt/C, with improvement in terms of current density for methanol electrooxidation. Comparing potentiostatic measurements, we found that glycerol produces lower pseudo-stationary current densities than ethanol and methanol on both catalysts, with greatest values found for methanol electrooxidation on Pt/C. Otherwise, the GNRs remarkably enhance the stability of the catalyst for all the reactions, by increasing the stability of the current density during successive potential cycles, and by preventing the loss of electrochemically active surface area by avoiding carbon corrosion and Pt detachment. Moreover, we showed that the stability of the NPs depends on the biomass-derived alcohol used. The solution containing methanol reveals itself the most aggressive electrochemical environment to the catalyst, impacting in the decrease of surface area, while glycerol is less aggressive. Hence, the different products formed at the interface electrode/solution might lead to a different electrochemical environment, which plays an important role on the stability of the catalysts.The authors acknowledge financial assistance from CNPq (grant no. 454516/2014-2), FUNDECT (grant no. 026/2015), FAPESP (grant no. 2016/01365-0), CAPES, FINEP, and FAPESP.Peer reviewe
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Rarity of monodominance in hyperdiverse Amazonian forests.
Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such "monodominant" forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors
Phosphorus–iron interaction in sediments : can an electrode minimize phosphorus release from sediments?
All restoration strategies to mitigate eutrophication depend on the success of phosphorus (P) removal from the water body. Therefore, the inputs from the watershed and from the enriched sediments, that were the sink of most P that has been discharged in the water body, should be controlled. In sediments, iron (hydr)oxides minerals are potent repositories of P and the release of P into the water column may occur upon dissolution of the iron (hydr)oxides mediated by iron reducing bacteria. Several species of these bacteria are also known as electroactive microorganisms and have been recently identified in lake sediments. This capacity of bacteria to transfer electrons to electrodes, producing electricity from the oxidation of organic matter, might play a role on P release in sediments. In the present work it is discussed the relationship between phosphorus and iron cycling as well as the application of an electrode to work as external electron acceptor in sediments, in order to prevent metal bound P dissolution under anoxic conditions.The authors are grateful to two anonymous reviewers of a previous version of the manuscript for the constructive comments and suggestions. The authors also acknowledge the Grant SFRH/BPD/80528/2011 from the Foundation for Science and Technology, Portugal, awarded to Gilberto Martins
Geographic patterns of tree dispersal modes in Amazonia and their ecological correlates
Unidad de excelencia María de Maeztu CEX2019-000940-MAim: To investigate the geographic patterns and ecological correlates in the geographic distribution of the most common tree dispersal modes in Amazonia (endozoochory, synzoochory, anemochory and hydrochory). We examined if the proportional abundance of these dispersal modes could be explained by the availability of dispersal agents (disperser-availability hypothesis) and/or the availability of resources for constructing zoochorous fruits (resource-availability hypothesis). Time period: Tree-inventory plots established between 1934 and 2019. Major taxa studied: Trees with a diameter at breast height (DBH) ≥ 9.55 cm. Location: Amazonia, here defined as the lowland rain forests of the Amazon River basin and the Guiana Shield. Methods: We assigned dispersal modes to a total of 5433 species and morphospecies within 1877 tree-inventory plots across terra-firme, seasonally flooded, and permanently flooded forests. We investigated geographic patterns in the proportional abundance of dispersal modes. We performed an abundance-weighted mean pairwise distance (MPD) test and fit generalized linear models (GLMs) to explain the geographic distribution of dispersal modes. Results: Anemochory was significantly, positively associated with mean annual wind speed, and hydrochory was significantly higher in flooded forests. Dispersal modes did not consistently show significant associations with the availability of resources for constructing zoochorous fruits. A lower dissimilarity in dispersal modes, resulting from a higher dominance of endozoochory, occurred in terra-firme forests (excluding podzols) compared to flooded forests. Main conclusions: The disperser-availability hypothesis was well supported for abiotic dispersal modes (anemochory and hydrochory). The availability of resources for constructing zoochorous fruits seems an unlikely explanation for the distribution of dispersal modes in Amazonia. The association between frugivores and the proportional abundance of zoochory requires further research, as tree recruitment not only depends on dispersal vectors but also on conditions that favour or limit seedling recruitment across forest types
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