1,720,960 research outputs found
Enhanced photocatalytic hydrogen evolution via ball-milled PtO<sub>2</sub>/TiO<sub>2</sub> heterojunction photocatalyst: an alternative approach for efficient energy production
No full textA novel PtO2/TiO2 heterojunction photocatalyst was synthesized via ball milling and investigated for its potential in photocatalytic hydrogen production. The effects of PtO2 loading, catalyst concentration, and sacrificial agent concentration on the hydrogen evolution rate (HER) were systematically evaluated. The results indicate that increasing the PtO2 concentration in the catalyst significantly enhances the hydrogen production rate, reaching a maximum value of approximately 54 mmol∙h−1∙g−1 at a PtO2 concentration of 20 wt%. The effect of the sacrificial agent concentration on the hydrogen production exhibited a Langmuir-Hinshelwood behavior with constant hydrogen production rates at sacrificial agent concentrations greater than 2.5 M. The experimental results were described by a kinetic model to shed light on the reforming mechanism. Finally, the stability of the photocatalyst was confirmed through four consecutive cycle tests. This synergistic integration of experimental and modelling analyses provides a robust platform for uncovering mechanistic details of photocatalytic hydrogen generation using a photocatalyst synthesized through a facile preparation method.</p
Mechanistic insights into hydrogen evolution from methanol photoreforming on metal-loaded Anatase: development of a microkinetic model
Full text linkA microkinetic model was developed to describe the kinetics of hydrogen production via methanol photoreforming under UV and visible light irradiations. The model integrates DFT calculations with experimental results to uncover mechanistic insights on the photoreforming process. The reaction mechanism and its governing rate coefficients were embedded into the design equation of a batch reactor to simulate the experimentally measured hydrogen evolution rates. Methanol exhibits a moderate reaction barrier to the methoxy anion (0.39 eV) and a low barrier to formaldehyde (0.16 eV), which serves as a key intermediate enabling multiple reaction pathways. In contrast, water shows moderately accessible formation of the hydroxyl radical (reaction barrier: 0.43 eV) while the formation of oxygen radicals is less accessible (reaction barrier: 0.66 eV). Radical coupling results in the exothermic formation of formic acid. Direct oxidation of formaldehyde yields carbon monoxide, whereas its hydroxylation leads to the formation of carbon dioxide. The microkinetic model incorporating DFT-derived energies showed good agreement with experimental methanol photoreforming data. The production of CH2O closely follows that of H2, emerging as the most kinetically accessible oxidation pathway. The production of O2 is predicted to be negligible across all metals, and the production of CO and CO2 is predicted to be minimal. These findings demonstrate the power of microkinetic modelling methodologies to accurately predict photocatalytic behaviour and guide the rational design of more efficient hydrogen evolution systems.</p
Understanding and tuning Fe‐doping on Zn–Fe layered double hydroxide particle and photocatalytic properties
No full textZn-based layered double hydroxides (LDHs) are promising photocatalytic materials, but their synthesis faces environmental and economic challenges. Oxidative ionothermal synthesis (OIS) offers a green route for zinc oxide synthesis using ionic liquids. To reduce costs, the OIS method uses recovered zinc-containing mixed metal systems, such as electric arc furnace dust, instead of pure metallic Zn. Understanding the interaction of Zn with impure metals during oxidation is essential. This study employs 1-Butyl-3-methylimidazolium chloride ([BMIM]Cl) as the solvent and Fe-doped metallic Zn, the most common waste-stream metal, as the starting material. This study applies quartz crystal microbalance with dissipation to monitor product formation, and X-ray diffraction and scanning electron microscopy to characterize composition and morphology. Results show that FeCl2 doping accelerates the reaction, transforming simonkolleite to Zn–Fe LDH with tunable morphologies. A reaction mechanism for Zn in [BMIM]Cl with FeCl2 is proposed. Photocatalytic hydrogen production tests reveal a favorable hydrogen evolution rate of 20.9 μmol h−1 g−1 with 0.45 M FeCl2 doping, attributed to improved surface structure and crystallinity of the hydrotalcite
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
Unravelling the photoactivity of metal-loaded TiO2 for hydrogen production: Insights from a combined experimental and computational analysis
Full text linkDespite being the most employed material for photocatalytic hydrogen generation, TiO2 suffers limitations such as a high rate of electron-hole recombination and poor light absorption in the visible spectrum. Among the various strategies developed to overcome these drawbacks, combining TiO2 with a metal co-catalyst emerged as one of the most promising. In this study, we integrated experimental findings, advanced characterization techniques, and computational methods to shed light on how different noble metals influence the enhancement of the photocatalytic activity of TiO2. Among the tested noble metal co-catalysts, the hydrogen production rate under UV and visible light irradiation followed the trend Pt > Au ≈ Pd > Ag > bare TiO2, with Pt-decorated TiO2 exhibiting a hydrogen production rate of 28 mmol/h g. The noble metals were found to significantly suppress the electron-hole recombination rate compared to bare TiO2. Upon photodeposition, Pd and Pt formed the smallest nanoparticles with average sizes of 13.4 nm and 4.1 nm, respectively. Computational analyses were conducted to rationalize the difference in nanoparticle sizes by analyzing the binding and cohesive energies of the metal clusters on the TiO2 surface. Additionally, calculations demonstrated the strong interaction of Pt, Au, and Pd nanoclusters with adsorbed hydrogen, with Pt achieving the closest-to-zero Gibbs free energy of hydrogen adsorption and displaying the most polar interaction with hydrogen. These findings align closely with the observed hydrogen production rates, where UV/Vis-driven hydrogen production is governed by the coupling of hydrogen radicals on the co-catalyst surface, while visible-light-driven production is limited by charge carrier lifetimes
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