16 research outputs found
Sulfur-Functionalized Mesoporous Carbons as Sulfur Hosts in Li–S Batteries: Increasing the Affinity of Polysulfide Intermediates to Enhance Performance
The Li–S system offers a tantalizing battery for electric vehicles and renewable energy storage due to its high theoretical capacity of 1675 mAh g^(–1) and its employment of abundant and available materials. One major challenge in this system stems from the formation of soluble polysulfides during the reduction of S_8, the active cathode material, during discharge. The ability to deploy this system hinges on the ability to control the behavior of these polysulfides by containing them in the cathode and allowing for further redox. Here, we exploit the high surface areas and good electrical conductivity of mesoporous carbons (MC) to achieve high sulfur utilization while functionalizing the MC with sulfur (S–MC) in order to modify the surface chemistry and attract polysulfides to the carbon material. S–MC materials show enhanced capacity and cyclability trending as a function of sulfur functionality, specifically a 50% enhancement in discharge capacity is observed at high cycles (60–100 cycles). Impedance spectroscopy suggests that the S-MC materials exhibit a lower charge-transfer resistance compared with MC materials which allows for more efficient electrochemistry with species in solution at the cathode. Isothermal titration calorimetry shows that the change in surface chemistry from unfunctionalized to S-functionalized carbons results in an increased affinity of the polysulfide intermediates for the S–MC materials, which is the likely cause for enhanced cyclability
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Evidence confirms an anthropic origin of Amazonian Dark Earths.
Arising from: Silva et al. Nature Communications https://doi.org/10.1038/s41467-020-20184-2 (2021
Self-Assembly of Linear Porphyrin Oligomers into Well-Defined Aggregates
Conjugated zinc porphyrin oligomers of various lengths
are shown
to form well-defined planar aggregates at low temperatures. The aggregation
occurs over a narrow temperature interval (170–150 K) and is
accompanied by dramatic changes in the electronic absorption and emission
spectra. Similar changes are found in J-aggregates in which the transition
dipole moments of aggregated chromophores couple to form a new and
intense transition in the absorption spectrum, red shifted from the
monomeric chromophore band. For the present porphyrin oligomers, the
dramatic absorption changes are not associated with the formation
of large aggregates, but rather with the dimerization accompanied
by planarization of the oligomers. Free oligomers have a broad distribution
of porphyrin–porphyrin dihedral angles and show a broad and
unstructured absorption spectrum. As the oligomers stack to form aggregates,
they planarize and the width of the conformational distribution is
reduced to include virtually only the planar conformers, resulting
in the observed change of the absorption spectrum. No experimental
evidence for the formation of large aggregates was found, while a
small aggregate, probably only dimer, is supported by the minor changes
of the fluorescence rate constant upon aggregation and the fact that
pyridine has no significant effect on the formation of this aggregate,
which otherwise is very effective for inhibiting aggregation of zinc
porphyrin oligomers. Compared to most porphyrin aggregates, which
show broad absorption spectra and quenched fluorescence, these aggregates
give sharp absorption and emission spectra with little change in the
fluorescence quantum yield. Similar aggregates were also observed
for oligomers substituted with both a fullerene electron acceptor
and a ferrocene donor. The results presented here will be potentially
useful as tools to understand how electron transfer and delocalization
processes are influenced by molecular order/disorder transitions
A produção do conhecimento no serviço social brasileiro a partir de Antonio Gramsci: um estudo dos programas de pós-graduação na área do serviço social (2010-2015)
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Sócio-Econômico, Programa de Pós-Graduação em Serviço Social, Florianópolis, 2017.Esta dissertação tem como tema o pensamento de Antonio Gramsci e sua presença no Serviço Social brasileiro. O objeto da pesquisa abrange a produção teórica e acadêmica (teses de doutorado) calcada nos conceitos de Gramsci nos Programas de Pós-Graduação no período 2010-2015. Trata-se de uma pesquisa teórica e bibliográfica, realizada por meio da perspectiva crítico-dialética. Os objetivos são: a) identificar as teses que utilizaram o pensamento de Gramsci, produzidas nos PPGSS com conceitos CAPES 5, 6 e 7; b) mapear, em resumos, sumários e/ou introdução das teses, os conceitos gramscianos mais utilizados, assim como a seleção de temas e recortes; c) compreender em que medida os conceitos possibilitam realizar mediações com o Serviço Social; d) identificar, a partir das referências bibliográficas, a utilização das obras de Gramsci e de seus intérpretes; e) contribuir com o fortalecimento do debate teórico-metodológico, prático-político e crítico do Serviço Social. O mapeamento das teses possibilitou identificar os principais conceitos como Estado, sociedade civil, hegemonia, cultura, intelectuais, ideologia, classes subalternas, americanismo, fordismo, guerra de movimento, guerra de posição, revolução passiva e transformismo. Os resultados da investigação indicam que a produção de conhecimento pautada pelo pensamento de Gramsci cresceu de forma significativa no período pesquisado, relacionando-se aos temas: Políticas Públicas (assistência social, agricultura, educação, cultura, mobilidade urbana, segurança alimentar, segurança pública, saúde, mídia e informação e trabalho); Feminismo e Gênero; Participação Popular e Controle Social; Movimentos Sociais e Sindicais; Serviço Social (formação, exercício profissional e fundamentos teórico-metodológicos); Mundo do Trabalho (reestruturação produtiva); Neodesenvolvimentismo e Social-liberalismo nos governos Lula; Organização Popular; e Direito e Justiça. Percebe-se que as fontes de pesquisa abarcam a edição temática togliattiana (1971) e, de forma crescente, as edições brasileiras de Escritos Políticos I e II (2004) e Cadernos do Cárcere (1999-2002) (6 volumes) e a edição crítica dos Cadernos (1975; 1977) do Instituto Gramsci, organizada por Valentino Gerratana. As edições citadas nas pesquisas selecionadas foram: Maquiavel, a política e o estado moderno (1968; 1978; 1980; 1984; 1988; 1989; 1991), A concepção dialética da história (1978; 1987; 1989; 1995), Os intelectuais e a organização da cultura (1968; 1978; 1979; 1982; 1987) e Literatura e Vida Nacional (1977). Além dos textos A questão meridional (1987), Obras escolhidas (1978), Americanismo e fordismo (2008) e La Política y el estado (1971). Os principais artigos citados são Os católicos italianos (1918); Sindicalismo e conselhos (1919); Sindicatos e conselhos I (1919); O partido e a revolução (1919); Democracia operária (1919); Democracia e fascismo (1924) e O partido comunista I (1929).Abstract : The theme of the dissertation is the presence of Antonio Gramsci s thought within the Brazilian social service. The research s object covers the theoretical academic production of Doctoral thesis tracing gramscian s categories, alongside postgraduate programs, across the period 2010-15. It is a theoretical and bibliographical research, carried out through a critical-dialectic perspective. The objectives of the research are: a) identify thesis produced in PPGSS with CAPES 5, 6, 7 scores which indicate the utilisation of Gramsci s philosophy; b) map, through summaries, abstracts and/or thesis introductions, the most utilised categories, themes and approaches; c) understand how the gramscians categories allow the realisation of mediations with the Social Service; d) identify, starting from the bibliographic references, the utilisation of Gramsci s work and of its interpreters; e) contribute to the reinforcement of the theoretical-methodological and practical-political debate of the Social Service. The analysis of the thesis allowed the identification of the main gramscians categories, them being: State, civil society, hegemony, culture, intellectuals, ideology, subordinate classes, Americanism, Fordism, war of position, war of manoeuvre, passive revolution and transformism. The main results of the investigation denote that, within the researched period, the production of knowledge guided by Antonio Gramsci s philosophy rose significantly in relation to themes such as: Public Policy (welfare, agriculture, education, culture, urban mobility, food security, public security, health, media, information and employment); Feminism and Gender studies; Public/popular participationand Social Control; Trade Unions and Social Movements; Social Service (education/training, professional practice); Employment (production restructuring); Neo-development and social-liberalism in Lula s governments; Popular organisation, Rights and Justice. In relation to the themes and designations present in Summary, Introduction and bibliographic references, the search sources embrace the thematic togliattiana s edition and, increasingly, the Brazilian edition of Political Writings (I and II) and of Prison notebooks (six volumes) (1999-2002) and the critical edition of Cadernos de Cárcere (1975; 1977) of the Gramsci Institute, organized by Valentino Gerratana. The thematic editions cited were: Selected Works (1978); Dialectical conception of history (1966, 1978, 1987; 1989; 1995); Machiavelli, Politics and the Modern State (1968; 1978; 1980; 1984; 1988; 1989; 1991); and The Intellectuals and the Organization of Culture (1968; 1978; 1979; 1982; 1987); The Southern Question (1987) ; La Política y el estado (1971) and Americanism and Fordism (2008). The main articles cited are The Italian Catholics (1918); Syndicalism and advice (1919); Unions and councils I (1919); The Party and the Revolution (1919); Workers' democracy (1919); Democracy and Fascism (1924) and The Communist Party I (1929)
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Sulfur-functionalized mesoporous carbons as sulfur hosts in Li-S batteries: increasing the affinity of polysulfide intermediates to enhance performance.
The Li-S system offers a tantalizing battery for electric vehicles and renewable energy storage due to its high theoretical capacity of 1675 mAh g(-1) and its employment of abundant and available materials. One major challenge in this system stems from the formation of soluble polysulfides during the reduction of S8, the active cathode material, during discharge. The ability to deploy this system hinges on the ability to control the behavior of these polysulfides by containing them in the cathode and allowing for further redox. Here, we exploit the high surface areas and good electrical conductivity of mesoporous carbons (MC) to achieve high sulfur utilization while functionalizing the MC with sulfur (S-MC) in order to modify the surface chemistry and attract polysulfides to the carbon material. S-MC materials show enhanced capacity and cyclability trending as a function of sulfur functionality, specifically a 50% enhancement in discharge capacity is observed at high cycles (60-100 cycles). Impedance spectroscopy suggests that the S-MC materials exhibit a lower charge-transfer resistance compared with MC materials which allows for more efficient electrochemistry with species in solution at the cathode. Isothermal titration calorimetry shows that the change in surface chemistry from unfunctionalized to S-functionalized carbons results in an increased affinity of the polysulfide intermediates for the S-MC materials, which is the likely cause for enhanced cyclability
A Discrete Three-Layer Stack Aggregate of a Linear Porphyrin Tetramer: Solution-Phase Structure Elucidation by NMR and X‑ray Scattering
Formation
of stacked aggregates can dramatically alter the properties
of aromatic π-systems, yet the solution-phase structure elucidation
of these aggregates is often impossible because broad distributions
of species are formed, giving uninformative spectroscopic data. Here,
we show that a butadiyne-linked zinc porphyrin tetramer forms a remarkably
well-defined aggregate, consisting of exactly three molecules, in
a parallel stacked arrangement (in chloroform at room temperature;
concentration 1 mM–0.1 μM). The aggregate has a mass
of 14.7 kDa. Unlike most previously reported aggregates, it gives
sharp NMR resonances and aggregation is in slow exchange on the NMR
time scale. The structure was elucidated using a range of NMR techniques,
including diffusion-editing, <sup>1</sup>H–<sup>29</sup>Si
HMBC, <sup>1</sup>H–<sup>1</sup>H COSY, TOCSY and NOESY, and <sup>1</sup>H–<sup>13</sup>C edited HSQC spectroscopy. Surprisingly,
the <sup>1</sup>H–<sup>1</sup>H COSY spectrum revealed many
long-range residual dipolar couplings (RDCs), and detailed analysis
of magnetic field-induced <sup>1</sup>H–<sup>13</sup>C RDCs
provided further evidence for the structural model. The size and shape
of the aggregate is supported by small-angle X-ray scattering (SAXS)
data. It adopts a geometry that maximizes van der Waals contact between
the porphyrins, while avoiding clashes between side chains. The need
for interdigitation of the side chains prevents formation of stacks
consisting of more than three layers. Although a detailed analysis
has only been carried out for one compound (the tetramer), comparison
with the NMR spectra of other oligomers indicates that they form similar
three-layer stacks. In all cases, aggregation can be prevented by
addition of pyridine, although at low pyridine concentrations, disaggregation
takes many hours to reach equilibrium
Sulfur-Functionalized Mesoporous Carbons as Sulfur Hosts in Li–S Batteries: Increasing the Affinity of Polysulfide Intermediates to Enhance Performance
The Li–S system offers a tantalizing battery for electric vehicles and renewable energy storage due to its high theoretical capacity of 1675 mAh g<sup>–1</sup> and its employment of abundant and available materials. One major challenge in this system stems from the formation of soluble polysulfides during the reduction of S<sub>8</sub>, the active cathode material, during discharge. The ability to deploy this system hinges on the ability to control the behavior of these polysulfides by containing them in the cathode and allowing for further redox. Here, we exploit the high surface areas and good electrical conductivity of mesoporous carbons (MC) to achieve high sulfur utilization while functionalizing the MC with sulfur (S–MC) in order to modify the surface chemistry and attract polysulfides to the carbon material. S–MC materials show enhanced capacity and cyclability trending as a function of sulfur functionality, specifically a 50% enhancement in discharge capacity is observed at high cycles (60–100 cycles). Impedance spectroscopy suggests that the S-MC materials exhibit a lower charge-transfer resistance compared with MC materials which allows for more efficient electrochemistry with species in solution at the cathode. Isothermal titration calorimetry shows that the change in surface chemistry from unfunctionalized to S-functionalized carbons results in an increased affinity of the polysulfide intermediates for the S–MC materials, which is the likely cause for enhanced cyclability
Revisiting thiol-yne chemistry: Selective and efficient monoaddition for block and graft copolymer formation
International audienceno abstrac
Reactivity Ratios and Mechanistic Insight for Anionic Ring-Opening Copolymerization of Epoxides
Reactivity ratios were evaluated for anionic ring-opening
copolymerizations
of ethylene oxide (EO) with either allyl glycidyl ether (AGE) or ethylene
glycol vinyl glycidyl ether (EGVGE) using a benzyl alkoxide initiator.
The chemical shift for the benzylic protons of the initiator, as measured
by <sup>1</sup>H NMR spectroscopy, were observed to be sensitive to
the sequence of the first two monomers added to the initiator during
polymer growth. Using a simple kinetic model for initiation and the
first propagation step, reactivity ratios for the copolymerization
of AGE and EGVGE with EO could be determined by analysis of the <sup>1</sup>H NMR spectroscopy for the resulting copolymer. For the copolymerization
between EO and AGE, the reactivity ratios were determined to be <i>r</i><sub>AGE</sub> = 1.31 ± 0.26 and <i>r</i><sub>EO</sub> = 0.54 ± 0.03, while for EO and EGVGE, the reactivity
ratios were <i>r</i><sub>EGVGE</sub> = 3.50 ± 0.90
and <i>r</i><sub>EO</sub> = 0.32 ± 0.10. These ratios
were consistent with the compositional drift observed in the copolymerization
between EO and EGVGE, with EGVGE being consumed early in the copolymerization.
These experimental results, combined with density functional calculations,
allowed a mechanism for oxyanionic ring-opening polymerization that
begins with coordination of the Lewis basic epoxide to the cation
to be proposed. The calculated transition-state energies agree qualitatively
with the observed relative rates for polymerization
Revisiting thiol-yne chemistry: Selective and efficient monoaddition for block and graft copolymer formation
International audienceno abstrac