Effect of the A cation size disorder and synthesis conditions on the properties of an iron perovskite series

Póster presentado en The Energy and Materials Research Conference - EMR2015 celebrado en Madrid (España) entre el 25-27 de febrero de 2015

Tunable Multiresponsive Methacrylic Acid Based Inverse Opal Hydrogels Prepared by Controlling the Synthesis Conditions

Methacrylic acid based inverse opal hydrogels (MIOHs) have been prepared by controlling the synthesis conditions, including cross-linker content, solvent content, and water content in solvent mixtures to explore the effect of the synthesis conditions (especially solvent content and mixture) on the response performance. Various response events (pH, solvent, ionic strength, 1,4-phenylenediamine dihydrochloride (PDA) response) have been investigated. For pH, solvent response, the same response behaviors have been observed: both the increased solvent (only ethanol) content and the enhanced water content in solvent will lead to the reduced response level of MIOHs compared to that of the increased cross-linker content. However, two different kinds of response behaviors for ionic strength response have been found by adjusting the synthesis conditions. The kinetics of pH response shows characteristics of a diffusion-limited process, and the equilibrium response time is about 20 min, which cannot be reduced by changing the synthesis conditions.

Effects of Synthesis Conditions on the Nanostructure of Hybrid Sols Produced by the Hydrolytic Condensation of (3-Methacryloxypropyl)trimethoxysilane

Polysilsesquioxanes containing methacrylate pendant groups were prepared by the sol-gel process through hydrolysis and condensation of (3-methacryloxypropyl)trimethoxysilane (MPTS) dissolved in a methanol/methyl methacrylate (MMA) mixture. The effects of different water, MMA, and methanol contents, as well as of pH, on the nanoscopic and local structures of the system, at advanced stages of the condensation reaction, were studied by small-angle X-ray scattering (SAXS) and (29)Si nuclear magnetic resonance (NMR) spectroscopy, respectively. SAXS results indicate that the nanoscopic features of the hybrid sol could be described by a hierarchical model composed of two levels, namely (i) silsesquioxane (SSQO) nanoparticles Surrounded by the methacrylate pendant groups and the methanol/MMA mixture. and (ii) aggregation zones or islands containing correlated SSQO nanoparticles, embedded in the liquid medium. The (29)Si NMR results Show that the inner Structures of SSQO nanoparticles produced at pH 1 and 3 were built Up of polyhedral structures. mainly cagelike octamers and small linear oligomers, respectively. Irrespective of MMA and methanol contents, for a [H(2)O]/[MPTS] ratio higher than or equal to 1, the SSQO nailoparticles produced at pH I exhibit an average condensation degree (CD approximate to 69-87%) and average radius of gyration (R(g) approximate to 2.5 angstrom) larger than those produced at pH 3 (CD approximate to 48-67% and R(g) approximate to 1.5 angstrom). Methanol appears to act as a redispersion agent, by decreasing the number of particles inside the aggregation zones, while the addition of MMA induces a swelling of the aggregation zones.

Study of ethanol electro-oxidation in acid environment on Pt(3)Sn/C anode catalysts prepared by a modified polymeric precursor method under controlled synthesis conditions

A carbon-supported binary Pt(3)Sn catalyst has been prepared using a modified polymeric precursor method under controlled synthesis conditions This material was characterized using X-ray diffraction (XRD). and the results indicate that 23% (of a possible 25%) of Sn is alloyed with Pt, forming a dominant Pt(3)Sn phase. Transmission election microscopy (TEM) shows good dispersion of the electrocatalyst and small particle sizes (3 6 nm +/- 1 nm) The polarization curves for a direct ethanol fuel cell using Pt(3)Sn/C as the anode demonstrated Improved performance compared to that of a PtSn/C E-TEK. especially in the intrinsic resistance-controlled and mass transfer regions. This behavior is probably associated with the Pt(3)Sn phase. The maximum power density for the Pt(3)Sn/C electrocatalyst (58 mW cm(-2)) is nearly twice that of a PtSn/C E-TEK electrocatalyst (33 mW cm(-2)) This behavior is attributed to the presence of a mixed Pt(9)Sn and Pt(3)Sn alloy phase in the commercial catalysts (C) 2009 Elsevier B V All rights reserved

Influence of Hydrothermal Synthesis Conditions and Device Configuration on the Photoresponse of UV Sensors Based on ZnO Nanorods

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of synthesis conditions on carbonate entrapment in perovskite SrSnO(3)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effects of Synthesis Conditions on the Nanostructure of Hybrid Sols Produced by the Hydrolytic Condensation of (3-Methacryloxypropyl)trimethoxysilane

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effects of synthesis conditions on the nanostructre of CexZr1-xO2 mesoporous ceramics.

CexZr1-xO2 (0.5 ≤ x ≤ 0.9) were synthesized with Zr and Ce chloride precursors, using the triblock copolymer Pluronic P123 and HCl (2 mol/L). The pH adjustment was performed in two ways: synthesis A used 11.4 mL of a NH4OH solution added at once to the initial mixture, composed by metal precursors and template in HCl; synthesis B was done by dripping slowly until the change of pH value (between 3 and 6). In this work, CexZr1-xO2 samples synthesized by these two processes are compared. The effects of pH values in materials characteristics were also evaluated. These samples were analysed by X-Ray Diffraction (XRD) with Rietveld refinement, and Nitrogen Adsorption/Desorption. In both processes, the studied materials presented two crystalline phases of CexZr1-xO2 solid solution: cubic and tetragonal. The synthesis A also presented a tetragonal phase of ZrO2. The average crystallite size and the Brunauer- Emmett-Teller (BET) surface area are bigger in process A. Both processes give samples with a mesoporous structure.

Oligodeoxynucleotide synthesis using protecting groups and a linker cleavable under non-nucleophilic conditions

Oligodeoxynucleotides (ODNs) containing latent electrophilic groups can be highly useful in antisense drug development and many other applications such as chemical biology and medicine, where covalent cross-linking of ODNs with mRNA, protein and ODN is required. However, such ODN analogues cannot be synthesized using traditional technologies due to the strongly nucleophilic conditions used in traditional deprotection/cleavage process. To solve this long lasting and highly challenging problem in nucleic acid chemistry, I used the 1,3-dithian-2-yl-methoxycarbonyl (Dmoc) function to protect the exo-amino groups on the nucleobases dA, dC and dG, and to design the linker between the nascent ODN and solid support. These protecting groups and linker are completely stable under all ODN synthesis conditions, but can be readily cleaved under non-nucleophilic and nearly neutral conditions. As a result, the new ODN synthesis technology is universally useful for the synthesis of electrophilic ODNs. The dissertation is mainly comprised of two portions. In the first portion, the development of the Dmoc-based linker for ODN synthesis will be described. The construction of the dT-Dmoc-linker required a total of seven steps to synthesize. The linker was then anchored to the solid support―controlled pore glass (CPG). In the second portion, the syntheses of Dmoc-protected phosphoramidites ODN synthesis monomers including Dmoc-dC-amidite, Dmoc-dA-amidite, Dmoc-dG-amidite are described. The protection of dC and dA with 1,3-dithian-2-yl-methyl 4-nitrophenyl carbonate proceeded smoothly giving Dmoc-dC and Dmoc-dA in good yields. However, when the same acylation procedure was applied for the synthesis of Dmoc-dG, very low yield was obtained. This problem was later solved using a highly innovative and environmentally benign procedure, which is expected to be widely useful for the acylation of the exo-amino groups on nucleoside bases. The reactions to convert the Dmoc-protected nucleosides to phosphoramidite monomers proceeded smoothly with high yields. Using the Dmoc phosphoramidite monomers dA, dC, dG and the commercially available dT, and the Dmoc linker, four ODN sequences were synthesized. In all cases, excellent coupling yields were obtained. ODN deprotection/cleavage was achieved by using non-nucleophilic oxidative conditions. The new technology is predicted to be universally useful for the synthesis of ODNs containing one or more electrophilic functionalities.

An efficient approach for the direct synthesis of lithium niobate powders

Lithium niobate powders from the raw powders of Li2 O5 are directly synthesized by a combustion method with urea fuel. The synthesis parameters (e.g. the calcination temperature, calcination time, and urea-to-(Li2 CO3 + Nb2 O5) quantity ratio) are studied to reveal the optimized synthesis conditions for preparing high-quality lithium niobate powders. In our present work, it is found that a urea-to-(Li2 CO3 + Nb2 O5) ratio close to 3, calcination temperature at 550-600 degrees and reaction time around 2.5h may lead to high-quality lithium niobate powsers. The microstructure of synthesized powders is further studied; a possible mechanism of the involved reactions is also proposed.

The synthesis and spectroscopic characterisation of hydrotalcite formed from aluminate solutions

Raman spectroscopy has been used to characterise nine hydrotalcites prepared from aluminate and magnesium solutions (magnesium chloride and seawater). The aluminate hydrotalcites are proposed to have the following formula Mg6Al2(OH)16(CO32-).xH2O, Mg6Al2(OH)16(CO32-,SO42-).xH2O, and Mg6Al2(OH)16(SO42-).xH2O. The synthesis of these hydrotalcites using seawater results in the intercalation of sulfate anions into the hydrotalcite interlayer. The spectra have been used to assess the molecular assembly of the cations and anions in the hydrotalcite structures. The spectra have been conveniently subdivided into spectral features based upon the carbonate anion, the hydroxyl units and water units. This investigation has shown the ideal conditions to form hydrotalcite from aluminate solutions is at pH 14 using magnesium chloride. Changes in synthesis conditions resulted in the formation of impurity products aragonite, thenardite, and gypsum.

The effect of synthesis temperature on the formation of hydrotalcites in Bayer liquor : a vibrational spectroscopic analysis

The seawater neutralisation process is currently used in the Alumina industry to reduce the pH and dissolved metal concentrations in bauxite refinery residues, through the precipitation of Mg, Al, and Ca hydroxide and carbonate minerals. This neutralisation method is very similar to the co-precipitation method used to synthesise hydrotalcite (Mg6Al2(OH)16CO3•4H2O). This study looks at the effect of temperature on the type of precipitates that form from the seawater neutralisation process of Bayer liquor. The Bayer precipitates have been characterised by a variety of techniques, including X-ray diffraction, Raman spectroscopy and infrared spectroscopy. The mineralogical composition of Bayer precipitates largely includes hydrotalcite, hydromagnesite, and calcium carbonate species. XRD determined that Bayer hydrotalcites that are synthesised at 55 °C have a larger interlayer distance, indicating more anions are removed from Bayer liquor. Vibrational spectroscopic techniques have identified an increase in hydrogen bond strength for precipitates formed at 55 °C, suggesting the formation of a more stable Bayer hydrotalcite. Raman spectroscopy identified the intercalation of sulfate and carbonate anions into Bayer hydrotalcites using these synthesis conditions.

Synthesis of metastable, wurzite-based zinc oxide-cobalt(II) oxide solid solutions by spray pyrolysis

Aqueous solutions of acetates and nitrates of zinc and cobalt have been spray decomposed to study the production of extended solid solutions in the ZnO-CoO system. Examination of the products of a variety of synthesis conditions indicates that up to 70% CoO may be retained in the solid solution in the wurzite phase, even though a comparison of the equilibrium solubility in the phase diagram might be expected to favor the formation of a rock-salt-based solid solution.

Morphological Evolution During Synthesis of New AlPO4 Center dot H2O Crystal

A new crystal of aluminophosphate, AIPO(4)(.)H(2)O, is synthesized from two-batch aqueous solution under hydrothermal conditions. Three types of the crystal habits, i.e. the tetragonal double pyramid, the tetragonal prism and the plate-type tetragonal prism, are found from batch-A solution. Two types of the crystal habits, i.e. the hexagonal pyramid and the strip-type tetragonal prism, are found from batch-B solution. The change of crystal morphology is originated from the fluctuation of the synthesis conditions, such as the supersaturation, the temperature and the impurity content. It causes change of the step energies, the defect density and the step roughness, and further, change of the growth rates. Since the crystal morphology is sensitive to the mass transport mechanism, the crystal habits could be changed under the microgravity.

Imidazolium-Based Organic Structure Directing Agents for the Synthesis of Microporous Materials

The central theme of this thesis is the use of imidazolium-based organic structure directing agents (OSDAs) in microporous materials synthesis. Imidazoliums are advantageous OSDAs as they are relatively inexpensive and simple to prepare, show robust stability under microporous material synthesis conditions, have led to a wide range of products, and have many permutations in structure that can be explored. The work I present involves the use of mono-, di-, and triquaternary imidazolium-based OSDAs in a wide variety of microporous material syntheses. Much of this work was motivated by successful computational predictions (Chapter 2) that led me to continue to explore these types of OSDAs. Some of the important discoveries with these OSDAs include the following: 1) Experimental evaluation and confirmation of a computational method that predicted a new OSDA for pure-silica STW, a desired framework containing helical pores that was previously very difficult to synthesize. 2) Discovery of a number of new imidazolium OSDAs to synthesize zeolite RTH, a zeolite desired for both the methanol-to-olefins reaction as well as NOX reduction in exhaust gases. This discovery enables the use of RTH for many additional investigations as the previous OSDA used to make this framework was difficult to synthesize, such that no large scale preparations would be practical. 3) The synthesis of pure-silica RTH by topotactic condensation from a layered precursor (denoted CIT-10), that can also be pillared to make a new framework material with an expanded pore system, denoted CIT-11, that can be calcined to form a new microporous material, denoted CIT-12. CIT-10 is also interesting since it is the first layered material to contain 8 membered rings through the layers, making it potentially useful in separations if delamination methods can be developed. 4) The synthesis of a new microporous material, denoted CIT-7 (framework code CSV) that contains a 2-dimensional system of 8 and 10 membered rings with a large cage at channel intersections. This material is especially important since it can be synthesized as a pure-silica framework under low-water, fluoride-mediated synthesis conditions, and as an aluminosilicate material under hydroxide mediated conditions. 5) The synthesis of high-silica heulandite (HEU) by topotactic condensation as well as direct synthesis, demonstrating new, more hydrothermally stable compositions of a previously known framework. 6) The synthesis of germanosilicate and aluminophosphate LTA using a triquaternary OSDA. All of these materials show the diverse range of products that can be formed from OSDAs that can be prepared by straightforward syntheses and have made many of these materials accessible for the first time under facile zeolite synthesis conditions.