1,721,136 research outputs found
Oxygen vacancies and interfaces enhancing photocatalytic hydrogen production in mesoporous CNT/TiO2 hybrids
No full textWe demonstrate a unique route towards hierarchical assemblies of mesoporous TiO2 and CNT/TiO2 photocatalysts by a combination of electrospinning and sol–gel methods. The resulting materials exhibit a mesoporous network of highly crystalline, well-connected inorganic nanocrystals with an order of magnitude higher photocatalytic activity than individualised TiO2 nanoparticles. The in-situ combination of small amounts of MWCNTs with TiO2 to form an electrospun CNT/TiO2 hybrid further enhanced the oxide photoactivity considerably, reaching hydrogen evolution rates of 1218 μmol/h in water splitting in the presence of sacrificial reagents under UV irradiation. We also discuss the effect of oxygen vacancies on the oxide crystallisation and phase transformation. These vacancies lead to inter-bandgap states and a lower flat band potential that facilitates the photocatalytic process
Elucidation of a Core–Shell Structure in Phenyl-Grafted Carbon Nitride/TiO2 Nanohybrids for Visible-Light-Mediated H2 Production with Simultaneous Rhodamine B Degradation
Full text linkDual-functional photocatalysts help to maximize
resource utilization in water remediation, but often they are visiblelight-
inactive, toxic, and cost-intensive. Herein, a type-II heterojunction
visible-light-active photocatalyst is reported for tandem
degradation of Rhodamine B and generation of H2. A Rhodamine B
degradation rate of 2.3 × 10−2 min−1 and H2 production activity of
5789 μmol h−1 g−1 are shown. The hybrid shows a gradient core−
shell morphology with a visible - light-absorbing phenyl-modified
carbon nitride (PhCN) core and a porous PhCN/TiO2 outer shell,
resulting in an enhanced interaction between the catalyst and the
surroundings. The nanoscale crystallization of TiO2 on PhCN’s
surface, shifts the triazine network structure, while autoclave
treatments further increase the band gap and suppress charge
carrier recombination. The influence of nanoscale morphological changes on photocatalytic activity was examined by varying the
component ratios and thermal treatments, highlighting the strong correlation between the nanoscale architecture and the enhanced catalytic activity. This work provides a detailed guide to the exploration of environmentally friendly dual-functional photocatalysts
Catalytic multivariable metal-organic frameworks for lithium-sulfur batteries
No full textMetal-organic frameworks (MOFs) hold potential for promoting the redox reaction of sulfur species (RRS) and suppressing the shuttle effect in lithium–sulfur batteries (LSBs). However, except for a limited number of frameworks, most MOFs are found to be inert in accelerating RRS, which is largely related to the fact that their design principles and mechanism of catalysis have not been fully understood. Systematic density functional theory (DFT) calculations and experimental results reveal that the lack of exposed polar catalytic sites restricts MOF’s potential in promoting RRS. Herein, based on a series of multivariable MOFs containing ligands with different thermal stability, selective ligand removal and ligand exchange (LE) strategies were applied successively to expose the catalytic metal clusters and introduce extra adsorption sites, rendering inert MOFs into catalytic ones. Such post-modified multivariable MOFs were shown to yield LSBs with remarkably improved specific capacity and cycling stability realizing 7.9 mAh cm−2 of capacity after 100 cycles at high sulfur loading of 8.1 mg·cm−2 under a lean electrolyte condition. The universal strategy proposed in this work will guide the design of catalytic MOFs for RRS and promote the development of advanced catalysts for high-performance LSBs
Synthesis and application of nature-inspired materials for photocatalytic processes
No full textTato práce zkoumá design a syntézu inovativních, vitaminem B2 inspirovaných, molekulárních organických fotosenzitizerů neobsahujících kovy, s cílem přispět novými poznatky do oblasti udržitelné výroby energie a fotodynamické terapie při léčbě rakoviny. Tyto -konjugované organické materiály mají jedinečné optické, redoxní a fotosenzitizační vlastnosti, přičemž organická syntéza umožňuje jejich vylepšení na molekulární úrovni a přizpůsobení pro energetiku a medicinské aplikace První část práce zkoumá potenciál flavinů jako fotosenzitizerů pro umělou fotosyntézu, přičemž zdůrazňuje jejich schopnost absorbovat viditelné světlo a pohánět výrobu vodíku. Nový syntetický přístup zlepšuje tradiční metody přípravy a vede k sérii nových flavinových derivátů. Studium vývoje vodíku používá systém složený z flavinového fotosenzitizerů, ko-katalyzátoru a obětního činidla, který je ozařován vybranou vlnovou délkou. Navrhovaná práce poskytuje důležité mechanistické poznatky o účinnosti flavinů prostřednictvím studie zhášení za účelem objasnění mechanismu výroby vodíku. Komplexní optimalizační studie odhalila patnáctinásobné zvýšení výtěžků vodíku vztaženo k 1 mg flavinu A-Pyr-Bu. Tento fotosenzitizér také prokázal výjimečnou účinnost a fotostabilitu, dosahující zjevného kvantového výtěžku 10,3 % při 415 nm při využití optimalizovaných podmínek. Na druhé straně derivát A-Phe-Bu vykazoval vyšší počáteční aktivitu dosahujíc zjevného kvantového výtěžku 13,7 % při 415 nm, i když byl náchylnější k fotodegradaci. Navzdory výzvám spojeným s fotodegradací a kvazi-homogenním uspořádáním použitým pro studii, tato zjištění zdůrazňují významný potenciál flavinových fotosenzitizerů pro aplikace v oblasti produkce zelené energie. Druhá část studie zkoumá ve vodě rozpustné flavinové analogy a jejich terapeutický potenciál ve fotodynamické terapii. Cytotoxicita těchto sloučenin byla hodnocena pomocí AlamarBlue testu na zdravých i rakovinných buňkách. Mezi hodnocenými deriváty vykazovaly A-Pyr-TEG a A-Phe-TEG slibné bezpečnostní profily a terapeutickou účinnost, což naznačuje jejich potenciál jako účinných látek při léčbě rakoviny
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Towards single-site photocatalysis: design of non-noble-metal-based systems
Full text linkDue to the world’s current energy crisis and the inevitable depletion of fossil fuels, finding alternative energy sources has become ever more important. Photocatalysis, also known as artificial photosynthesis, allows the transformation of solar to chemical energy by facilitating non-spontaneous chemical reactions with the aid of light irradiation and a photocatalyst. Through photocatalysis, the sun’s energy – an inexhaustible energy source – can be stored in the chemical bonds of so-called “solar fuels” (e.g. hydrogen or hydrocarbons) by means of water splitting or CO2 reduction reactions, respectively. However, after 60 years of targeted research, real-world applications of heterogeneous photocatalysis are still limited by the insufficient efficiency and predictability of contemporary catalytic systems.Heterogenous single-metal-site catalysts (HSMSCs) feature many advantages over their bulkier counterparts as a result of their ability to bridge the qualities of homo- and heterogeneous catalysis. When relying on the concept of HSMSCs, maximized atom utilization efficiency and accessibility of the active sites renders excellent catalytic performances (homogeneous trait), while stability and recyclability stay preserved (heterogeneous trait).Applying HSMSCs in photocatalysis is a rather novel approach, especially considering earth-abundant co-catalysts, which are still underexplored. Besides, the use of HSMSCs allows to construct more unique and selective co-catalysts to address the challenges of complex multielectron catalytic reactions. Moreover, applying the single-site concept to noble metals – which show superior catalytic activities but are scarce in the earth’s crust – could make their implementation more feasible for large-scale applications.In this Thesis we synthesize heterogeneous single-metal-site photocatalysts following the “isolation strategy” through an adsorption-limited wet impregnation process by using TiO2 as model support and earth-abundant (Cu and Ni) and noble (Pt and Au) metals as co-catalysts. The catalysts are characterized by IR and UV-vis spectroscopy for qualitative analysis, TXRF for determination of the real loadings of the active species, and TEM for resolving the atomic structure and morphology of the samples. We investigate the different adsorption/deposition behaviors of the precursor species on the support and the influence of light during synthesis. Noble metals undergo photodeposition to form nanoparticles under ambient-light, whereas earth-abundant metals rather stay as complexed species on the substrate’s surface. To further promote the formation and stabilization of single-site species, we modify the support’s surface with PO4 groups. The resulting PO4/TiO2 shows enhanced adsorption of metal precursors and stronger structural changes in the co-catalyst species thus confirming a crucial role of the surface charge and chemistry on the single-site stabilization.Furthermore, we evaluate the performance of our photocatalysts through photocatalytic hydrogen evolution reaction (HER) experiments and discuss the obtained activity trends (in terms of H2 evolution rates and turnover frequency values) in light of different mathematical models. All investigated photocatalysts consistently follow our non-linear model upon decreasing the loadings, which speaks for an alteration in the co-catalyst’s size/morphology towards smaller, perhaps even single-site-like species. When using the modified PO4/TiO2 substrate, the activity trend of Pt > Au > Cu > Ni gets less pronounced, and the best-performing earth-abundant systems based on Cu become comparable to the Au-based samples. Finally, we demonstrate that the activity trend – when normalized per cost of precursor – gets inverted, hence, suggesting that earth-abundant co-catalysts could open up new frontiers for practical applications
2D-2D PhCN/WS2 exfoliated nanosheets for visible-light hydrogen production: A platinum-free Co-catalyst approach
Full text linkSubstituting fossil fuels with green energy sources such as H2 is one of the prime objectives of achieving a sustainable and carbon-neutral future. In this work, a noble-metal-free 2D-2D hybrid photocatalyst PhCN/WS2 is reported for application in hydrogen production under visible-light irradiation, where WS2 is utilized as an
environmentally friendly co-catalyst. The synthesis and characterization of 2D Phenyl-modified carbon nitride (PhCN) and 2D WS2 via liquid-phase exfoliation are systematically investigated. The effectiveness of a solventmediated self-assembly is highlighted, and the effect of WS2 flake size on the photocatalytic activity of the hybrid is examined. The hybridization of exfoliated PhCN with two-dimensional (2D) WS2 demonstrates a 42-fold enhancement in hydrogen evolution compared to exfoliated PhCN alone under visible light. This improvement is attributed to the role of WS2 as an effective hydrogen evolution reaction (HER) co-catalyst. The utilization of larger WS2 nanoflakes proved to be ideal to establish fast charge carrier transportation networks
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Bridging hetero- and homogeneous photocatalysis: anchoring of Ru-based water oxidation catalyst on CNT-metal oxide hybrid for overall water splitting
No full text- …
