1,721,024 research outputs found
Design of mesoporous silica at low acid concentrations in triblock copolymer-butanol-water systems
No full textAssembly of hybrid mesophases through the combination of amphiphilic block copolymers, acting as structure-directing agents, and silicon sources using low acid catalyst concentration regimes is a versatile strategy to produce large quantities of high-quality ordered large-pore mesoporous silicas in a very reproducible manner. Controlling structural and textural properties is proven to be straightforward at low HCl concentrations with the adjustment of synthesis gel composition and the option of adding co-structure-directing molecules. In this account, we illustrate how various types of large-pore mesoporous silica can easily be prepared in high phase purity with tailored pore dimensions and tailored level of framework interconnectivity. Silica mesophases with two-dimensional hexagonal (p6mm) and three-dimensional cubic (Fm (3) over barm, Im (3) over barm and la (3) over bard) symmetries are generated in aqueous solution by employing HCl concentrations in the range of 0.1-0.5 M and polyalkylene oxide-based triblock copolymers such as Pluronic P123 (EO20-PO70-EO20) and Pluronic F127 (EO106-PO70EO106). Characterizations by powder X-ray diffraction, nitrogen physisorption, and transmission electron microscopy show that the mesoporous materials all possess high specific surface areas, high pore volumes and readily tunable pore diameters in narrow distribution of sizes ranging from 4 to 12 nm. Furthermore, we discuss our recent advances achieved in order to extend widely the phase domains in which single mesostructures are formed. Emphasis is put on the first synthetic product phase diagrams obtained in SiO2-triblock copolymerBuOH-H2O systems, with tuning amounts of butanol and silica source correspondingly. It is expected that the extended phase domains will allow designed synthesis of mesoporous silicas with targeted characteristics, offering vast prospects for future applications.The work was supported by the Korea Ministry of Science and Technology and the School
of Molecular Science through the Brain Korea 21 project. F. Kleitz thanks the Canadian Government for the Canada Research Chair in Functional Nanostructured Materials.
Synchrotron radiation XRD experiments at PLS were supported in part by MOST and POSTECH
Phase domain of the cubic im3m mesoporous silica in the EO106PO70EO106-butanol-H2O system
No full textn-Butanol has been chosen as an organic additive in the SiO2-EO106PO70EO106-H2O system at low HCl concentrations, for the generation of large-pore mesoporous silicas with easily tailored textural and structural properties. As opposed to previous reports on syntheses of cubic mesoporous silica that are usually performed in a very narrow composition range, we report now the possibility of preparing large-pore cagelike mesoporous silicas in a wide range of synthesis mixture compositions. Particularly, the cubic Im3m silica with large interconnected cagelike pores (SBA-16) can easily be synthesized with controlled pore sizes and wall thicknesses, depending upon the synthesis mixture composition. The primary mesopore volume of the SBA-16 cages can be tuned from 0.27 to 0.56 cm(3) g(-1), and the mesopore size is shown to range from 4.7 to 7.2 nm, by performing a simple adjustment of the starting mixture composition. With the synthesis parameters varied, we describe the first complete diagram of the product phase domains obtained for silica mesophases in a SiO2-EO106PO70E106-butanol-H2O system. Other ordered mesophases also observed in this system are the face-centered cubic Fm3m silica mesophase and a 2D hexagonal-like mesostructure. Importantly here, the use of a low acid catalyst concentration regime allowed the preparation of silica mesophases in almost thermodynamically controlled conditions because of slow condensation kinetics of the inorganics. Such conditions enabled the introduction of n-butanol as the phase-controlling agent in the system, providing efficient tuning of the mesophase topology. The description of the phase domains provides a future basis for the design of large-pore mesoporous silicas with tailored textural and structural properties. Mesoporous samples obtained within the composition ranges of the phase domains are characterized by powder X-ray diffraction (PXRD) and nitrogen physisorption measurements.F. K. thanks the Canadian Government
for the Canada Research Chair in Functional Nanostructured Materials (2005-2010). The work was supported by the Korea Ministry of Science and Technology and the School of Molecular Science through the Brain Korea 21 project. Synchrotron radiation XRD experiments at PLS were supported in part by MOST and POSTECH
Cubic Ia3d large mesoporous silica: synthesis and replication to platinum nanowires, carbon nanorods and carbon nanotubes
No full textA new synthesis route to high-quality large mesoporous cubic Ia3d silica is reported, utilizing a triblock copolymer ( EO20PO70EO20) - butanol mixture for the structure direction in aqueous solution.The work was supported by the Korea Ministry of Science and Technology and the School of Molecular Science through the BK21 project
Facile synthesis of high quality mesoporous SBA-15 with enhanced control of the porous network connectivity and wall thickness
No full textConvenient and commercially viable synthesis conditions are described, providing efficient and reproducible control of pore connectivity and pore wall thickness for the synthesis of high quality SBA-15 mesoporous silica
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
Understanding Selectivity of Mesoporous Silica-Grafted Diglycolamide-Type Ligands in the Solid-Phase Extraction of Rare Earths
Full text linkRare earth elements (REEs) and their compounds are essential for rapidly developing modern technologies. These materials are especially critical in the area of green/sustainable energy; however, only very high-purity fractions are appropriate for these applications. Yet, achieving efficient REE separation and purification in an economically and environmentally effective way remains a challenge. Moreover, current extraction technologies often generate large amounts of undesirable wastes. In that perspective, the development of selective, reusable, and extremely efficient sorbents is needed. Among numerous ligands used in the liquid-liquid extraction (LLE) process, the diglycolamide-based (DGA) ligands play a leading role. Although these ligands display notable extraction performance in the liquid phase, their extractive chemistry is not widely studied when such ligands are tethered to a solid support. A detailed understanding of the relationship between chemical structure and function (i.e., extraction selectivity) at the molecular level is still missing although it is a key factor for the development of advanced sorbents with tailored selectivity. Herein, a series of functionalized mesoporous silica (KIT-6) solid phases were investigated as sorbents for the selective extraction of REEs. To better understand the extraction behavior of these sorbents, different spectroscopic techniques (solid-state NMR, X-ray photoelectron spectroscopy, XPS, and Fourier transform infrared spectroscopy, FT-IR) were implemented. The obtained spectroscopic results provide useful insights into the chemical environment and reactivity of the chelating ligand anchored on the KIT-6 support. Furthermore, it can be suggested that depending on the extracted metal and/or structure of the ligand and its attachment to KIT-6, different functional groups (i.e., C= O, N-H, or silanols) act as the main adsorption centers and preferentially capture targeted elements, which in turn may be associated with the different selectivity of the synthesized sorbents. Thus, by determining how metals interact with different supports, we aim to better understand the solid-phase extraction process of hybrid (organo)silica sorbents and design better extraction materials
INSIGHTS INTO THE CO2 ADSORPTION PROPERTIES OF NITROGEN-CONTAINING ORDERED MESOPOROUS CARBONS
Full text linkThe increase of global CO2 concentration is the main responsible for global warming. Nitrogen-containing ordered mesoporous carbons (NOMCs) are here proposed as CO2 adsorbents, thanks to their adsorption ability and selectivity in simulated flue gases mixtures. In this work, NOMCs are synthesized as replications of an ordered mesoporous silica hard template, using the well-known nanocasting route. This method is convenient for achieving a pore architecture composed of both micro- and mesopores able to promote at the same time improved capture performances and fast kinetics of gas diffusion, respectively. One of the drawbacks of the synthesis of NOMCs is the use of toxic carbon/nitrogen sources or the addition of post-synthesis treatments for the nitrogen doping process.
A more sustainable approach is proposed in this work, using eco-friendly sources as nitrogen-rich carbon precursors. The effect of the pyrolysis temperature (varied from 600 to 900 °C) on the development of microporosity and N incorporation was related to pure CO2 adsorption and selectivity in CO2/N2 mixtures (20/80 v/v).
A maximum CO2 adsorption capacity of 1.47 mmol g-1 was achieved by the sample pyrolized at the highest temperature (i.e., 900°C) at 30 °C / 0.9 bar / pure CO2, while a CO2 uptake of 0.82 mmol g-1 was obtained by the sample pyrolized at the lowest temperature (i.e., 600 °C) at 35 °C / 1 bar / 20 % CO2.
The enhancement in pure CO2 adsorption is due to the increase of the micropore content. On the contrary, a lower pyrolysis temperature (600 °C) allowed for the retention of a higher amount of N, beneficial for the selective adsorption of CO2 in presence of N2
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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