1,720,963 research outputs found
Synthesis of Carbon Dots for medical and photocatalytic applications
No full textCarbon dots (CDs) are a novel carbon-based nanomaterial that draws a great attention in the last decade. The easy way of synthesis and the cheapest nature of the precursors used, stimulate a lot of scientist to propose new way of synthesis and applications. Notwithstanding the number of paper published, a systematic and reproducible way of synthesis is not yet been achieved, as well as a common definition of the resulting nanomaterials and their properties. In this thesis, the synthetic protocols and the characterization procedures used for the CDs will be deeply investigated in order to apply the nanomaterials in different applications. In particular, carbon dots synthesized from fully biocompatible precursors such as glucose, fructose and ascorbic acid, are characterized and employed for drug loading applications. The study reveals that the choice of the precursors is a crucial step because it affects the structural properties of the nanomaterials and the biological properties, revealing an unexpected toxicity for the fructose derived CDs, ascribable to its thermal degradation pathway. Furthermore, the drug loading capabilities were found to be correlated to the morphology of the nanoparticles, revealing the crucial role of the π-π interactions in achieving a loading up to 28 %wt for the glucose-based CDs. A second study was conduct on citric acid based CDs, in order to determine the best synthetic approach for photocatalytic applications. The nanoparticles synthesized both by hydrothermal and pyrolysis treatment, from sole citric acid and in combination with a nitrogen doping agent, were deeply characterized. The analysis reveals the difference in chemical, structural, and optical properties between the two synthetic methods. The photoreduction of methylviologen (MV) was used as model reaction to study the photocatalytic ability of the CDs, and the results reveal a relationship between the synthetic methods employed, the structural and optical properties of the CDs and their ability to act as a sensitizer. The amorphous nitrogen doped CDs reveals to be the best choice for this application with an initial rate conversion comparable to other reported in literature. The same CDs were also tested for the photocatalytic cleavage of C-O bonds in activated esters without the use of metals. The study reveals that CDs can successfully catalyze the reaction, with complete conversion and almost total selectivity. In addition, the CDs employed, shows different reactivity depending on the precursors and synthetic methods employed for their synthesis, with the same trend displayed for the MV photoreduction. This study highlights the ability of CDs to act as photosensitizer, without the addition of metals, in an organic reaction, opening a new scenario in the use of this nanomaterial in photocatalytic applications
Carbon dots as photocatalysts for organic synthesis: metal-free methylene–oxygen-bond photocleavage
No full textWe report for the first time that irradiation of four different citric acid-derived carbon dots (CDs), in the absence of any other redox mediators, promotes an organic reaction. In this proof-of-concept study methylene-oxygen bond reductive photocleavage in N-methyl-4-picolinium esters is demonstrated. Cyclic voltammetry and UV-Vis spectra of the CDs and of the esters indicate that photocleavage reactivity correlates with the redox properties and the relative energies expressed in the Fermi scale. A photo-fragmentation mechanism is proposed. This study offers a new possibility to employ inexpensive and readily available CDs to promote photo-organic reactions
Sustainable Strategies in the Synthesis of Lignin Nanoparticles for the Release of Active Compounds: A Comparison
No full textThe preparation of nanoparticles represents a powerful tool for lignin valorization, as it combines easy methodologies with high application potential. Different synthetic strategies and various lignin sources have been employed in the process. However, the great variability in the lignin structure prevents a direct comparison of the so far reported lignin nanoparticles (LNPs), especially as regards their physicochemical and functional properties. To this purpose, two green protocols, that is, solvent-antisolvent and hydrotropic, were optimized and used to generate LNPs from the same softwood kraft lignin. The nanomaterials were fully characterized to extrapolate structure/property relationships and reveal any differences in the mechanism of self-assembly. Furthermore, tests on methylene blue entrapment capacity and release behavior at two different pH values (2.0 and 7.4) evidenced a clear dependence on the LNPs characteristics and thus on the strategy adopted for their production
9 New perspectives in lignin valorization: Lignin-derived nanostructures
No full textLignin is undoubtedly one of the most interesting biomasses in terms of
high added-value materials obtainable from its valorization. As by-product of pulp
and paper industries and biorefineries, it is produced in large volumes and is readily
available at low cost. The unlocking of its full potential is therefore of crucial importance
in view of a sustainable growth based on circular economy paradigms. In this
context, the generation of lignin-based nanomaterials is attracting considerable
attention as the self-assembly characteristics of this biopolymer can be easily exploited,
thus avoiding time- and resource-consuming functionalization or purification
steps and, most importantly, preserving all its peculiar and unique features. In the
last years, many researchers have devoted their efforts toward the development of
more efficient and sustainable procedures for the synthesis of lignin-derived nanomaterials,
also expanding the possible applications thanks to the easy tunability of their
functional properties. In this contribution, the most important synthetic procedures
for the obtainment of lignin nanoparticles, nanocapsules and nanofibers are critically
revised and discussed, and the range of uses they have been tested for is presented
N-Doped Carbon Dot Hydrogels from Brewing Waste for Photocatalytic Wastewater Treatment
Full text linkThe brewery industry annually produces huge amounts of byproducts that represent an underutilized, yet valuable, source of biobased compounds. In this contribution, the two major beer wastes, that is, spent grains and spent yeasts, have been transformed into carbon dots (CDs) by a simple, scalable, and ecofriendly hydrothermal approach. The prepared CDs have been characterized from the chemical, morphological, and optical points of view, highlighting a high level of N-doping, because of the chemical composition of the starting material rich in proteins, photo-luminescence emission centered at 420 nm, and lifetime in the range of 5.5-7.5 ns. With the aim of producing a reusable catalytic system for wastewater treatment, CDs have been entrapped into a polyvinyl alcohol matrix and tested for their dye removal ability. The results demonstrate that methylene blue can be efficiently adsorbed from water solutions into the composite hydrogel and subsequently fully degraded by UV irradiation
Kraft (Nano)Lignin as Reactive Additive in Epoxy Polymer Bio-Composites
Full text linkThe demand for high-performance bio-based materials towards achieving more sustainable manufacturing and circular economy models is growing significantly. Kraft lignin (KL) is an abundant and highly functional aromatic/phenolic biopolymer, being the main side product of the pulp and paper industry, as well as of the more recent 2nd generation biorefineries. In this study, KL was incorporated into a glassy epoxy system based on the diglycidyl ether of bisphenol A (DGEBA) and an amine curing agent (Jeffamine D-230), being utilized as partial replacement of the curing agent and the DGEBA prepolymer or as a reactive additive. A D-230 replacement by pristine (unmodified) KL of up to 14 wt.% was achieved while KL-epoxy composites with up to 30 wt.% KL exhibited similar thermo-mechanical properties and substantially enhanced antioxidant properties compared to the neat epoxy polymer. Additionally, the effect of the KL particle size was investigated. Ball-milled kraft lignin (BMKL, 10 mu m) and nano-lignin (NLH, 220 nm) were, respectively, obtained after ball milling and ultrasonication and were studied as additives in the same epoxy system. Significantly improved dispersion and thermo-mechanical properties were obtained, mainly with nano-lignin, which exhibited fully transparent lignin-epoxy composites with higher tensile strength, storage modulus and glass transition temperature, even at 30 wt.% loadings. Lastly, KL lignin was glycidylized (GKL) and utilized as a bio-based epoxy prepolymer, achieving up to 38 wt.% replacement of fossil-based DGEBA. The GKL composites exhibited improved thermo-mechanical properties and transparency. All lignins were extensively characterized using NMR, TGA, GPC, and DLS techniques to correlate and justify the epoxy polymer characterization results
The Laccase-Lig Multienzymatic Multistep System in Lignin Valorization
No full textA laccase-Lig multienzymatic multistep system for lignin depolymerization was designed and developed. Studies were performed on pristine and fractionated lignins (Kraft and Organosolv) using a specific cascade of enzymes, that is, laccases from Bacillus licheniformis and from Funalia trogii, respectively for Kraft and Organosolv lignin, followed by the Lig system from Sphingobium sp. SYK-6 (β-etherases Lig E and Lig F, glutathione lyase Lig G). Careful elucidation of the structural modifications occurring in the residual lignins associated with the identification and quantification of the generated low-molecular-weight compounds showed that (i) the laccase-Lig system cleaves non-phenolic aryl glycerol β-O-4 aryl ether bonds, and (ii) the overall reactivity is heavily dependent on the individual lignin structure. More specifically, samples with low phenolic/aliphatic OH groups ratio undergo net depolymerization, while an increased phenolic/aliphatic OH ratio results in the polymerization of the residual lignin irrespective of its botanical origin and isolation process
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
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
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