556 research outputs found
Polyoxometalates immobilized onto mesoporous organically-modified silica aerogels for selective oxidation catalysis of anthracene - by Rami Ghassan Al-Oweini.
No full textThesis (M.S.)--American University of Beirut, Dept. of Chemistry, 2009.;"Advisor : Dr. Houssam El-Rassy, Assistant Professor, Chemistry--Member of Committee : Dr. Rabih Sultan, Professor , Chemistry--Member of Committee : Dr. Faraj Hasanayn, Associate ProBibliography : leaves 170-188.Novel surface organically-modified silica aerogels were synthesized and characte rized by FTIR spectroscopy and nitrogen adsorption-desorption experiments. The s urface modification of the silica aerogels was conducted with the help of a two- step sol-ge
Photocatalytic Water Oxidation by a Mixed-Valent (Mn3MnO3)-Mn-III-O-IV Manganese Oxo Core that Mimics the Natural Oxygen-Evolving Center
No full textThe functional core of oxygenic photosynthesis is in charge of catalytic water oxidation by a multi-redox MnIII/MnIV manifold that evolves through five electronic states (Si, where i=0-4). The synthetic model system of this catalytic cycle and of its S0→S4 intermediates is the expected turning point for artificial photosynthesis. The tetramanganese-substituted tungstosilicate [MnIII3MnIVO3(CH3COO)3(A-α-SiW9O34)]6- (Mn4POM) offers an unprecedented mimicry of the natural system in its reduced S0 state; it features a hybrid organic-inorganic coordination sphere and is anchored on a polyoxotungstate. Evidence for its photosynthetic properties when combined with [Ru(bpy)3]2+ and S2O82- is obtained by nanosecond laser flash photolysis; its S0→S1 transition within milliseconds and multiple-hole-accumulating properties were studied. Photocatalytic oxygen evolution is achieved in a buffered medium (pH 5) with a quantum efficiency of 1.7 %
Synthesis and Characterization of Multinuclear Manganese-Containing Polyoxotungstates for Homogeneous Water-Oxidation Catalysis
No full textPolyoxometalates are anionic, nano-sized metal-oxygen clusters of early transition metals in high oxidation states such as Mo6+, W6+, and V5+. The structural and compositional versatility of polyoxometalates is remarkable and is complemented by other tunable properties such as high stability, solubility and redox activity. Such properties render polyoxometalates highly desirable for catalytic studies such as homogeneous water-oxidation catalysis. Our group was able for the past thirteen years to synthesize a variety of polyanions containing multinuclear transition metal centers and clusters in acidic aqueous media. In particular, manganese-containing heteropolyoxotungstates are of special interest owed to the discovery of the active center responsible for the production of molecular oxygen from water in Photosystem II. The tetranuclear manganese oxygen-evolving center has motivated numerous attempts directed towards mimicking its structural or functional properties by designing a variety of manganese organic-based complexes. However have only resulted in poor activity being affected by thermal and oxidative degradation, unlike the robustness of polyoxometalates making them ideal frameworks for developing novel artificial photosystems.
Along these guidelines inspired by nature, the reaction of [MnIII8MnIV4O12(CH3COO)16(H2O)4] with [A-α-PW9O34]9- in a 1:2 molar ratio in aqueous, acidic medium resulted in a trimanganese(III)-containing, sandwich-type 18-tungsto-2-phosphate [MnIII3(H2O)5(A-α-PW9O34)2]9-. The polyanion crystallizes as a mixed potassium/cesium/guanidinium salt in the triclinic space group P-1, with cell parameters a = 13.1718(19) Å, b = 16.505(2) Å, c = 22.842(4) Å, α = 104.141(7)°, β = 106.267(8)°, γ = 101.369(6)°, V = 4430.6(12) Å3, and Z = 2. The polyanion comprises two [A-α-PW9O34]9- Keggin fragments linked via three MnIII ions, two of which are 6-ccordinated and one is 5-coordinated. The obtained polyanion salt was further characterized by IR, TGA, elemental analysis and magnetic measurements in the solid state. Electrochemical studies showed that the polyanion is both stable in solution and interesting for the elaboration of a water oxidation electrocatalyst, due to its MnIII oxidation wave governed by a mixed adsorption-diffusion regime, accompanied by electrode activation.
Five other manganese-containing Keggin-based tungstosilicates [MnII3(OH)3(H2O)3(A-α-SiW9O34)]7-, [MnIII3(OH)3(H2O)3(A-α-SiW9O34)]4-, [MnIII3(OH)3(H2O)3(A-β-SiW9O34)]4-, [MnIII3MnIVO3(CH3COO)3(A-α-SiW9O34)]6-, and [MnIII3MnIVO3(CH3COO)3(A-β-SiW9O34)]6- were also synthesized in aqueous medium by interaction of [A-α-SiW9O34]10- or [A-β-SiW9O34H]9- with either MnCl2·4H2O or [MnIII8MnIV4O12(CH3COO)16(H2O)4] under various reaction conditions. The obtained salts of these polyanions were further characterized in the solid state by IR, TGA, elemental analysis and magnetic studies, as well as in solution by electrochemistry. The tetranuclear manganese-containing 9-tungstosilicate, with its mixed-valence [MnIII3MnIVO3(CH3COO)3]4+ manganese assembly reminiscent of the oxygen evolving complex in Photosystem II, revealed high activity in photo-induced water splitting reactions. These results were further supported by several analytical techniques such as FT-IR, UV-Vis, electrochemical and conductiometric titration experiments. Additionally, in a similar fashion, the interaction of the same manganese coordination complex however with 9-tungstoarsenate(V) [A-α-AsVW9O34]9-, resulted into a novel mixed-valent decamanaganese-containing 36-tungsto-4aresenate(V) [MnIII6MnIV4O4(OH)12(H2O)12(A-β-AsVW9O34)4]22-, which might show interesting magnetic properties and photocatalytic activity in water-splitting due to the structurally appealing and electrocatalytically active [MnIII6MnIV4O4(OH)12(H2O)12]14+ core stabilized within the tungstoarsenate framework
Product Market Fit Material Serat Rami Sebagai Elemen Material Berkelanjutan Pada Penerapan Desain Furniture
No full textThe proliferation of research and applications of sustainable materials within society has seen a notable increase, leading to constant updates in product segments featuring sustainable materials. This trend is further supported by the growing awareness among the public regarding environmental degradation. Ramie fiber is one such sustainable material serving as an alternative to the dependence on cotton materials in the textile industry. Collaborating with Armonie Ronche from Universitas Padjajaran, the author undertook a series of processes to implement ramie fiber in a furniture product, emphasizing the creation of products with good market value. Over a period of four months, the development process resulted in a living room set where a combination of hemp fiber and teak wood served as the primary elements in the design, globally marketable, and modern Jengki-style furniture.Maraknya riset dan aplikasi material berkelanjutan yang digunakan oleh masyarakat semakin tinggi yang terlihat selalu muncul pembaruan pada segmen produk dengan material berkelanjutan. Hal ini juga didukung oleh tingkat kesadaran masyarakat akan kerusakan yang terjadi pada lingkungan sekitar. Serat rami merupakan salah satu material berkelanjutan sebagai alternatif dari ketergantungan penggunaan material kapas yang ada pada industri tekstil. Bekerjasama dengan Armonie Ronche dari Universitas Padjajaran penulis melakukan serangkaian proses pengimplementasian serat rami pada sebuah produk furniture dengan mengedepankan produk yang memiliki nilai jual yang baik di masyarakat. Selama empat bulan proses pengembangan didapatkan sebuah set ruang keluarga dimana padu padan antara material rami dengan material jati sebagai elemen utama dalam perancangan mebel bergaya modern jengki yang siap dipasarkan secara global
The politics of heterodoxy and the Kina Rami ascetics of Banaras
No full textThe Kina Rami, a sect of aghori ascetics, take their name from Kina Ram, a Rajput Sant of the seventeenth century. This thesis examines the history and reform of the Kina Ram sect while placing it within the larger framework of heterodox Shaivism. Using an anthropology of religion approach, the author uses fieldwork data and observations to discuss the sociopolitical issues related to extreme religious behavior within Indian religion and to mount a critique of scholarship that would seek to locate such behavior solely within the framework of Brahmanical Hinduism. Finally an overview is presented of the reform of the Kina Ram sect under the influence of the modern-day saint Avadhut Bhagwan Ram. The author demonstrates the contemporary use of traditional Kina Rami heterodox symbolism within the context of Avadhut Bhagwan Ram\u27s reformist organization, Sri Sarveshwari Samooh. While these reforms are demonstrated to be continuous with the traditional goals of the Kina Sect, they nonetheless represent a new compromise position in relation to the larger Brahmanical Hindu tradition
"Ramus Petri Rami" : figures martyrdom in the 1581 biography of Pierre de la Ramée by Nicolas de Nancel
No full textThis paper is devoted to the rhetorical analysis of Nicolas de Nancel’s Petri Rami Vita, which
is one of the most thorough biographies of Pierre de la Ramée (1515-1572), an early modern
French scholar, rhetorician, philosopher, and reformer of education. In the course of analysis,
the author points out intertextual relations between Nancel’s text and European tradition of
biographical writings which emerges from Plutarch’s Parallel Lives. The author reconstructs the
image of Ramus as a rhetorician and then concentrates his attention on the function and usefulness
of martyrological figures and images for further popularization of the Ramist doctrine
Photocatalytic degradation of atrazine by heteropolyoxotungstates
No full textAn elegant and eco-friendly photocatalytic degradation approach for the most commonly used herbicide, Atrazine (ATZ); allowed a selective and partial degradation into atrazine-2-hydroxy (Hydroxyatrazine, HAT), which was the sole obtained metabolite. The effect of tungstosilicates and tungstophosphates as photocatalysts under 60 min UV irradiation at two different wavelengths; 254 and 366 nm; was investigated by measuring the absorbance at 10-min intervals, using 720-UV spectrophotometry. ATZ conversion rate was the highest when irradiating with the higher-energy 254 nm UV light. This resulted into 54% degradation in the presence of the silicon-based α-Keggin dodecatungstosilicate [α-SiW12O40]4−, whereas 17% was decomposed in its absence. The nature of the heteroatom as well as the structural type of the studied polyoxometalates had a significant effect on the degradation percentage. Accordingly, 31% of ATZ was only decomposed in presence of the phosphorus-analogue [α-PW12O40]4− whereas the cyclic super-lacunary octatetracontatungstooctaphosphate [P8W48O184]40− increased the degradation to 41%
Surface characterization by nitrogen adsorption of silica aerogels synthesized from various Si(OR)4 and R″Si(OR′)3 precursors
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