1,721,012 research outputs found
Multivariate sensing of ions using machine learning and composite 2D-3D graphene oxide-hexacyanoferrate electrodes [Elektronisk resurs]
Full text linkThe conventional method for sensing relies on the development of highly selective materials capable of detecting specific target molecules or ions without interference from other species commonly found in real solutions. However, creating practical sensors that can effectively discriminate between analytes sharing similar chemistry presents significant challenges. To address this issue, we describe a novel approach utilizing an ensemble of four diverse amperometric sensors obtained for deposition of 2-dimensional graphene oxide nanosheets (GO) and 3-dimensional metal-organic frameworks (MOFs) based on redox active metal hexacyanoferrates. The multivariate signals obtained by the sensor array is used to train an artificial neural network (ANN) capable of analysing such complex inputs to accurately determine the concentrations of Na+ and K+ ions in solutions with varying ionic strengths. The sensing strategy is based on the differential intercalation and diffusion behaviour of Na+ and K+ ions within both GO and MOFs, resulting in distinct voltammetric signals. The neural network is trained using massive datasets comprising 327 variables as columns and over 4 million samples as rows. Following training, the sensor array demonstrates remarkable proficiency in accurately measuring the concentration of both ions present in solution, while a single sensor cannot discern between the signals generated by each ion. This ongoing work underscores the potential of integrating artificial intelligence with tunable materials to develop a new class of chemical sensors with enhanced discrimination capabilities, paving the way for more robust and versatile sensor technologies
Study and application of graphene oxide in the synthesis of 2,3-disubstituted quinolines via a Povarov multicomponent reaction and subsequent oxidation
No full textThe carbocatalyzed synthesis of 2,3-disubstituted quinolines is disclosed. This process involved a three-component Povarov reaction of anilines, aldehydes and electron-enriched enol ethers, which gave the substrate for the subsequent oxidation. Graphene oxide (GO) was exploited as a heterogeneous, metal-free and sustainable catalyst for both transformations. The multicomponent reaction proceeded under simple and mild reaction conditions, exhibited good functional group tolerance, and could be easily scaled up to the gram level. A selection of tetrahydroquinolines obtained was subsequently aromatized to quinolines. The multistep synthesis could also be performed as a one-pot procedure. Investigation of the real active sites of GO was carried out by performing control experiments and a by full characterization of the carbon material by X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance (ssNMR)
The removal efficiency of emerging organic contaminants{,} heavy metals and dyes: intrinsic limits at low concentrations
No full textIn this work{,} we exploit Langmuir adsorption isotherms to compare the performance of different materials (adsorbents) in removing organic contaminants (adsorbates) from water. The removal efficiency observed reaches an intrinsic limit at low concentrations. We also demonstrate quantitatively how multi-step adsorption processes achieve better purification efficiency than single-step adsorption performed using much smaller amounts of adsorbent material. We demonstrate how such performance is strongly affected by adsorbent concentration. Only the use of both the parameters obtained from Langmuir adsorption isotherm (Qm and KL) modelling allows one to compare materials tested under different experimental conditions by different groups{,} whereas most published reviews focus only on Qm which is rather limited for comparing the performance of different materials studied under different conditions. Finally{,} we present some guidelines for data reporting in future work and reviews
Synthesis of α‐Imino Amidines and 2,3‐Diamino Indolenines Using a One‐Pot Graphene Oxide‐Catalyzed Process
No full textThe acid-catalyzed three-component (3 C) UGI reaction of isocyanides, amines, and aldehydes generally gives α-amino amidines. Herein, we report the graphene oxide (GO)-promoted promoted 3 C Ugi reaction followed by a C−N bond oxidation to provide rapid access to α-imino amidines. GO plays a crucial role both in the multicomponent reaction and in the subsequent oxidation. Interestingly, α-imino amidines bearing electron-donating groups undergo spontaneous cyclization leading substituted 2,3-diamino indolenines. The scope of the process has been investigated with respect to all three components, and a comparison between the one-pot and sequential approaches is given. The major advantages of the developed methodology include one-pot synthesis, operational simplicity, high atom economy, broad substrate scope, multicomponent character, and applicability towards gram scale synthesis. Recovery and regeneration of GO and investigation of its real active sites has been performed by control experiments and X-ray photoelectron spectroscopy (XPS)
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
Accurate chemical analysis of graphene-based materials using X-ray photoelectron spectroscopy
Full text linkA simple, fast and general protocol for quantitative analysis of X-ray photoelectron spectroscopy (XPS) data provides accurate estimations of chemical species in graphene and related materials (GRMs). XPS data are commonly used to estimate the quality of and defects in graphene and graphene oxide (GO), by comparing carbon and oxygen 1s XPS peaks, obtaining an O/C ratio. This approach, however, cannot be used in the presence of extraneous oxygen contamination. The protocol, based on quantitative line-shape analysis of C 1s signals, uses asymmetric pseudo- Voigt line-shapes (APV), in contrast to Gaussian-based approaches conventionally used in fitting XPS spectra, thus allowing better accuracy in quantifying C 1s contributions from graphitic carbon (sp2), defects (sp3 carbon), carbons bonded to hydroxyl and epoxy groups, and from carbonyl and carboxyl groups. The APV protocol was evaluated on GRMs with O/C ratios ranging from 0.02 to 0.30 with film thicknesses from monolayers to bulk-like (>30nm) layers and also applied to previously published data, showing better results compared to those from conventional XPS fitting protocols. Based uniquely on C 1s data, the APV protocol can quantify O/C ratio and the presence of specific functional groups in GRMs even on SiOx, substrates, or in samples containing water
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
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