1,721,007 research outputs found
Covalent Lysozyme Immobilization on Enzymatic Cellulose Nanocrystals
Full text linkNanostructured materials represent promising substrates for biocatalyst immobilization and activation. Cellulose nanocrystals (CNCs), accessible from waste and/or renewable sources, are sustainable and biodegradable, show high specific surface area for anchoring a high number of enzymatic units, and high thermal and mechanical stability. In this work, we present a holistic enzyme-based approach to functional antibacterial materials by bioconjugation between the lysozyme from chicken egg white and enzymatic cellulose nanocrystals. The neutral CNCs were prepared by endoglucanase hydrolysis from Avicel. We explore the covalent immobilization of lysozyme on enzymatic CNCs and on their TEMPO oxidized derivatives (TO-CNCs), comparing immobilization yields, material properties, and enzymatic activities. The materials were characterized by X-ray diffractometry (XRD), attenuated total reflectance Fourier Transform infrared spectroscopy (ATR-FTIR), bicinchoninic acid (BCA) assay, field-emission scanning electron microscopy (FE-SEM) and dynamic light scattering (DLS). We demonstrate the higher overall efficiency of the immobilization process carried out on TO-CNCs, based on the success of covalent bonding and on the stability of the isolated bioconjugates.TEMPO-oxidized cellulose nanocrystals (TO-CNCs) are an excellent substrate for the covalent immobilization of lysozyme from chicken egg white. The bioconjugates are synthesized, isolated and characterized and are potential candidates as antibacterial materials. imag
High Yield Synthesis of Cellulose Nanocrystals From Avicel by Mechano-Enzymatic Approach
No full textCellulose nanocrystals are an important class of bio-based crystalline nanostructures, finding application in several technological fields, including paper and textile coating, biocomposite engineering, biocatalysts immobilization, etc. This study explores enzymatic hydrolysis of Avicel, using endoglucanase from Aspergillus niger, to find an environmentally friendly method to extract cellulose nanocrystals from cellulose sources. Enzymatic hydrolysis has the advantage of reduced energy consumption and higher environmental friendliness compared to acid hydrolysis. In this work, we report for the first time very high nanocrystals yield by combining mechanical pretreatment of the cellulose starting material with a ball miller and endoglucanase hydrolysis, as a result of an extensive optimization of reaction conditions. In particular, a ball milling pretreatment carried out for 50 minutes at 3 Hz, allowed to isolate enzymatic CNCs with 76 % yield and with crystallinity as high as 75 %. The materials were characterized by X-Ray diffractometry, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, dynamic light scattering, zeta potential and field emission scanning electron microscopy (FE-SEM). Their characteristics were compared with the properties of sulfated CNCs, prepared from Avicel by sulfuric acid hydrolysis. Our results are technologically relevant, as they contribute to the accessibility and sustainability of CNCs for a wide range of applications in various industries
Flexible Cellulose-Based Electrodes: Towards Eco-friendly All-paper Batteries
No full textIn the present work an easy paper-making technique is used for the manufacture of low cost and low environmental impact all-paper-based Li-ion cells. The cells are composed of two paper-like electrodes, prepared using micrometric-sized graphite (anode) and LiFePO4 (cathode) as active materials and truly natural microfibrillated cellulose as binder, and paper hand-sheets soaked in a standard liquid electrolyte solution as separator between them. The specific capacity obtained is even superior to that of standard PVdF-binded cell assembled with the same electrodes, and remains stable over prolonged cycling, indicating that the cellulose fibres do not affect the cycling stability. In this study, no organic solvents or synthetic polymer binders are used all along the production of the cell components which, in addition, can be easily re-dispersed in water by simple mechanical stirring as well as common paper handsheet
Method for preparing flexible self-supported electrodes (Procédé de préparation d'électrodes flexibles auto-supportées)
No full textThe present invention relates to a method of preparing flexible self-supported electrodes according to a method implementing refined cellulose fibres as a binder. It also concerns the negative or positive flexible self-supported electrode obtained according to such a method and a Li-ion battery in which at least one electrode is a flexible self-supported electrode. La présente invention concerne un procédé de préparation d'électrodes flexibles autosupportées selon un procédé mettant en œuvre des fibres de cellulose raffinées en tant que liant. Elle concerne également l'électrode flexible autosupportée négative ou positive obtenue selon un tel procédé et une batterie Li-ion dans laquelle au moins une électrode est une électrode flexible autosupportée
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Lignocellulosic Materials for the Next-Generation of Eco-Friendly Polymeric Energy Storage Devices
No full textIn the last 20 years, the Li-ion battery (LiB) market has rapidly grown thanks to the extensive diffusion of mobile electronics devices. In order to lower the cost and reduce the environmental impact of LiBs, efforts must be devoted to reduce the amount of inactive components in the cell, to substitute synthetic polymer binders / separators and organic solvents with low-cost and biosourced materials and to develop new eco-friendly processes for the manufacture of cell components. Natural nanoscale-microfibrillated cellulose (NMFC) fibers are readily available; they show stiffness, impressive mechanical robustness, low weight and, furthermore, their preparation process is easy and does not involve chemical reactions. They can significantly reinforce polymer electrolytes already at low filler loadings and also replace the commonly used PVdF as binder for self-standing and flexible electrodes, thus serving as a promising candidate for bio-composite production. Here we review the use of paper-making technique for manufacturing low cost bio-inspired all-paper Li-ion polymer cells, constituted by NMFC-binded paper-electrodes, and NMFC reinforced polymer electrolytes. The use of NMFC as filler/binder leads to produce high performing, safe and extremely flexible electrolytes for LiBs. No organic solvents or synthetic polymer binders are used during the entire electrode/electrolyte/cell preparation process. Materials and procedures are also extended to other “beyond-LiB” technologies, such as Na-ion and Li-S, thus demonstrating the possibility of obtaining “truly green” energy storage devices in the near future. Noteworthy, the all-paper-cell can be easily re-dispersed in water by simple mechanical stirring, as well as common paper handsheets and battery materials can be recovered using well-known water-based recycling process
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