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

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)

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, ¹H–²⁹Si HMBC, ¹H–¹H COSY, TOCSY and NOESY, and ¹H–¹³C edited HSQC spectroscopy. Surprisingly, the ¹H–¹H COSY spectrum revealed many long-range residual dipolar couplings (RDCs), and detailed analysis of magnetic field-induced ¹H–¹³C 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^–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

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 ¹H 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 ¹H NMR spectroscopy for the resulting copolymer. For the copolymerization between EO and AGE, the reactivity ratios were determined to be <i>r</i>_AGE = 1.31 ± 0.26 and <i>r</i>_EO = 0.54 ± 0.03, while for EO and EGVGE, the reactivity ratios were <i>r</i>_EGVGE = 3.50 ± 0.90 and <i>r</i>_EO = 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