Precipitation In Aqueous Solution Research Articles

Memory of chirality in J-type aggregates of an achiral perylene dianhydride dye created in a chiral asymmetric catalytic synthesis

Perylene dyes tend to form H-aggregates because of their large aromatic π-core and high hydrophobicity. We report here a chiral asymmetric catalytic synthesis of water-soluble chiral J-aggregates from highly hydrophobic and achiral perylene dianhydride (PDA). We propose to generate in situ aggregating hydrophobic species from a water soluble precursor so that it aggregates at a low concentration in solution within a predesigned microenvironment to stabilize the formed aggregates. Choosing PDA as an example, we generated it in situ from a water-soluble perylene-3,4,9,10-tetracarboxylate in acidic cetyltrimethylammonium bromide (CTAB) micelle solution, employing small molecule D- and/or L-tartaric acid as the chiral auxiliary. CD spectra of the PDA J-aggregates formed in the presence of D- and L-tartaric acid, respectively, were mirror images of each other. When the chiral auxiliary was absent, water-soluble J-aggregates of PDA were also obtained from acidic HCl-CTAB solution but they were then achiral. This confirms that the chirality of the J-aggregates is transferred from tartaric acid. Using an L-/D-tartaric acid mixture of varying ee as the chiral auxiliary, the exciton-coupled induced circular dichroism (ICD) signal of the formed PDA J-aggregates shows an “S”-shaped profile when plotted versus ee, indicating that chiral amplification occurs. Purified J-aggregates were found to contain PDA and CTAB, whereas tartaric acid was hardly detected, yet the ICD signals remained the same as those in the presence of tartaric acid before purification. This indicates memory in the J-aggregates of the chirality of tartaric acid. The ICD signal of the purified J-aggregates was also found to remain unchanged upon addition of a large excess of the other enantiomer of tartaric acid than the one used to induce the chirality, implying the imprinting of the chirality in the J-aggregates. The J-aggregates of PDA were shown to be positively charged from the polar heads of the CTAB surfactant molecules that help to disperse the aggregates and prevent their precipitation in aqueous solution. It was found that it is critical that the surfactant tail is long enough for the chiral J-aggregates to be created. This suggests that the hydrophobic tail might act as a pillar to support the J-aggregates that are driven by edge-edge hydrophobic interactions. With this in situ generation for the highly hydrophobic perylene dyes we succeeded in creating water soluble J-aggregates, chiral and achiral, in a controllable manner.

Photoactivity of Anatase–Rutile TiO2 Nanocrystalline Mixtures Obtained by Heat Treatment of Titanium Peroxide Gel

ABSTRACTNanosized titanium dioxide photocatalysts with anatase structure or mixture of anatase and rutile phases have been synthesized. Homogeneous precipitation of aqueous solutions containing TiOSO4 and ammonia and following treatment with H2O2 was used to prepare porous yellowish (Ti-Per) gel. The gel was lyophilized for 48h and (Ti-Per)LYO-powder was obtained. Single phase anatase TiO2 samples were prepared by heating of the (Ti-Per)LYO powder. The lamella-like particle morphology of TiO2 samples determined by SEM were stable in air up to 950°C.The structure evolution during heating of the starting (Ti-Per)LYO powder was studied by DTA and XRD analyses in overall temperature range of phase transformation. The morphology and microstucture characteristics were also obtained by HRTEM and BET methods. The photocatalytic activity of the sample titania TI-LYO/950 heated to 950ºC in air contained 78.4% anatase and 21.6% rutile was higher than standard Degussa P25. Titania sample TI-LYO/950 reveals the highest catalytic activity during the photocatalyzed degradation course of 4-chlorophenol in aqueous suspension under UV-irradiation.

Characterization of a calcium phospho-silicated apatite with iron oxide inclusions

An iron oxide containing calcium phosphate–silicate hydroxyapatite was synthesized by calcination at 900 °C of a sample obtained by precipitation in basic aqueous solution of Ca, P, Si, Fe and Mg containing acidic solution made from dissolution of natural minerals. XRD and FTIR were used for crystallographic characterization of the main apatitic phase. Its composition was determined using ICP-AES. EDX coupled with SEM and TEM evidenced the heterogeneity of this compound and the existence of iron–magnesium oxide. Magnetic analyses highlighted that this phase was non-stoichiometric magnesioferrite (Mg 1.2Fe 1.8O 3.9) spherical nanoparticles. Those analyses also put into evidence the role of calcination in synthesis. Carbonates detected by FTIR and estimated by SEM-EDX in non-calcinated sample were removed from apatitic structure, and crystallization of apatite was enhanced during heating. Moreover, there was phase segregation that led to magnesioferrite formation.

Synthesis of Soluble Poly(p-phenylene methylene) from Tribenzylborate by Acid-Catalyzed Polymerization

An acid-catalyzed polymerization of tribenzylborate (TBB) is described for the synthesis of soluble poly(phenylene methylene) (PPM). The polymerization proceeds via carbocationic mechanism with first-order kinetics with respect to TBB and 0.7th order with respect to acid concentration. The structure of PPMwascharacterized by 1 Hand 13 CNMRanalysis.ThermalpropertiesofPPMwereinvestigatedbyTGA and DSC, and thermally stable polymers displayed completly amorphous structure, which was attributed to nonrestricted rotation of the phenyl rings around bridged methylene units in the rodlike structure. PPM exhibits a broad fluorescence emission band with a maximum at 422 nm arising from the benzonoid transition. The extremely low dielectric constant of PPM suggests that these polymers can be used as polymer insulators. Attempts to bulk polymerization of TBB with0.2 to0.3 mL of H2SO4 ((H2SO4)/(TBB) 1/50) at room temperature resulted in explosions in each case, indicating highly exothermic nature of the polymerization. Low-molecular-weight polymer (M n: 960) isolated by precipitation in aqueous NaOH solution (3%) was shown to be entirely soluble in a wide range of organic solvents including CHCl 3 ,C H 2Cl2, toluene, benzene, and THF but

Optical characterization of CdS semiconductor nanoparticles capped with starch

Starch capped cadmium sulfide (CdS) nanoparticles were synthesized by aqueous solution precipitation. Starch added during the synthesis of nanoparticles resulted in cadmium-rich nanoparticles forming a stable complex with starch. The size of the CdS quantum dots was measured using high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The average diameter (d) of nanoparticles spanned the range 4.8±0.4 to 5.7±0.2nm when the pH of the solution was varied within the range 10–14. The main Raman phonon of CdS, the longitudinal optical mode located around 300cm−1, softens as diameter decreases, in accordance with theoretical predictions. In addition, the largest Raman response of starch, near 478cm−1, related with the important skeletal vibration modes of the starch pyranose ring, dominates the spectra of the CdS capped nanoparticles and also softens as the size decreases. This fact indicates a strain variation on CdS as a function of d which increases as the pH increases.

Aggregation kinetics of cerium oxide nanoparticles in monovalent and divalent electrolytes

As a result of the commercial availability and use of nanoparticulate cerium oxide, CeO 2, it is extremely likely that this material will be introduced into the environment requiring knowledge of its fate, transport and bioavailability in natural aquatic systems. To this end, this work probes the physicochemical interactions that govern the aggregation kinetics of cerium oxide nanoparticles using time-resolved dynamic light scattering (TR-DLS) over a range of monovalent, Na +, and divalent, Ca 2+, electrolyte concentrations. Sets of nanoparticles were synthesized by precipitation in aqueous solutions containing varying concentrations of methanol. The point of zero charge (pzc) of these nanoparticles changes as a result of synthesis method. Those produced in the absence of methanol had pzc = 6.5. As predicted by the theories of Derjaguin–Landau–Verwey–Overbeek (DLVO), both reaction-limited and diffusion-limited aggregation were observed in each solution type. The experimental critical coagulation concentrations (CCC) at pH 11.0 was ca. 80 mM and ca. 16 mM for the monovalent (NaCl) and divalent (CaCl 2) salts, respectively. DLVO theory proved to be an adequate predictor for the interactions between cerium oxide nanoparticles albeit the derived Hamaker constant of 1.0 × 10 −20 J was somewhat smaller than experimental Hamaker constants determined for other metal oxide nanoparticles. Deviations between experimental data and DLVO theory are discussed.

Kinetics of the self‐aggregation and film formation of poly‐L‐proline at high temperatures explored by circular dichroism spectroscopy

Poly-L-proline has been used as a model system for various purposes over a period of more than 60 years. Its relevance among the protein/peptide community stems from its use as a reference system for determining the conformational distributions of unfolded peptides and proteins, its use as a molecular ruler, and from the pivotal role of proline residues in conformational transitions and protein-protein interactions. While several studies indicate that polyproline can aggregate and precipitate in aqueous solution, a systematic study of the aggregation process is still outstanding. We found, by means of UV-circular dichroism and IR measurements, that polyproline is predominantly monomeric at room temperature at millimolar concentrations. Upon heating, the polypeptide stays in its monomeric state until the temperature reaches a threshold of ca. 60 degrees C. At higher temperatures, the peptide aggregates as a film on the inside surface of the employed cuvette. The process proceeds on a time scale of 10(3) s and can best be described by a bi-exponential relaxation function. The respective CD and IR spectra are qualitatively different from the canonical spectra of polyproline in aqueous solution, and are indicative of a highly packed state.

Photoluminescence of CdS nanoparticles embedded in a starch matrix

CdS nanoparticles were synthesized by precipitation in aqueous solution using starch as the capping molecule, and the effect of the pH of the solution on the optical absorption, photoluminescence, and size of the nanoparticles was studied. Absorption spectra, obtained by photoacoustic spectroscopy, indicated that the band gap energy of the crystalline nanoparticles decreased from 2.68 eV down to 2.48 eV by increasing the pH of the solution from 9 up to 14. The X-ray diffraction analysis revealed that the CdS nanoparticles were of zinc blende structure, and that the particle size increased from 1.35 nm up to 2.45 nm with increasing pH. In addition, temperature-dependent photoluminescence (PL) measurements of the capped material showed a blue-shift of the emission peak for temperatures higher than 150 K, indicating the influence of starch on the formation of defect levels on the surface of the CdS nanoparticles.

新潟大学における初動工学教育について 第3報 水溶液からの結晶析出課題事例

新潟大学における初動工学教育について 第3報 水溶液からの結晶析出課題事例

Synthesis, Characterization and HDS Activity of Carbon-Containing Ni–Mo Sulfide Nano-Spheres

Ni-promoted tetramethylammonium tetrathiomolybdate precursor was prepared by the aqueous solution precipitation method using (NH4)2MoS4, (CH3)4NBr and NiCl2.6H2O as raw materials. Carbon-containing Ni–Mo sulfide nanospheres, namely Ni/C1–MoS2, were obtained by ex situ thermal decomposition of the precursor under N2 atmosphere. Energy dispersive X-ray spectroscopy (EDS), low temperature N2 adsorption (BET method), X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) techniques were employed to characterize these as–synthesized sulfide particles. The results showed that the average size of solid Ni–Mo sulfide nanospheres, with surface composition MoNi0.40S0.73C1.43, is 75 nm and the solid structure leads to low surface area of Ni/C1–MoS2. In addition, the introduction of methyl chain improved the dispersion of nickel phases and resulted in C/Mo ratio, 1.4. By comparison with catalytic performance of the Ni/MoS2 catalyst counterpart, Ni/C1–MoS2 revealed lower HDS activity but higher direct desulfurization (DDS) selectivity. Lower stacking number of MoS2 slabs (5 layers) and shorter slabs length of MoS2 slabs (6 nm) explained higher DDS selectivity satisfactorily. The formation of carbon-containing Ni–Mo sulfide nanospheres was possibly due to surfactant effect of tetramethylammonium cations and the potential measure to increase their surface area was discussed as well in this work.

Study of structure and optical luminescence of C+6 (80 MeV) ion irradiated CdS: Fe system

Iron doped CdS nanocrystals have been synthesized by using aqueous solution precipitation method. Samples of CdS:Fe have been subjected to irradiation using C+6 (80 MeV) under of 1×1013 ions/cm2. For characterization, X-ray diffraction (XRD), Photoluminescence (PL) and Optical absorption studies have been performed. The system has been found in hexagonal phase having particle size distribution 18–20 nm. Photoluminescence intensity has been found to decrease, while optical band gap has been found to increase in irradiated samples.

Investigation of process parameters for the removal of polyvinyl alcohol from aqueous solution by iron electrocoagulation

The feasibility of polyvinyl alcohol (PVA) removal from aqueous solution was investigated using iron electrocoagulation. Several parameters, including type of electrode pair, applied voltage, supporting electrolytes, and solution temperature were investigated. The effects of applied voltage, supporting electrolyte, and solution temperature on PVA removal efficiency and specific energy consumption were also investigated. Experimental results indicated that a Fe/Al electrode pair was the most efficient choice of the four electrode pairs tested in terms of PVA removal efficiency. The optimum applied voltage, supporting electrolyte concentration, and solution temperature were found to be 10V, 100mg L−1 NaCl, and 298K, respectively. A pseudo-second-order kinetic model provided a good fit to experimental results at various applied voltages and solution temperatures. In addition, the activation energy was calculated to be 49.45J mol−1 based on pseudo-second-order rate constants from the Arrhenius equation, indicating that PVA precipitation in aqueous solution was attributable to the electrocoagulation process.

Tuning Surface Basic Properties of Nanocrystalline MgO by Controlling the Preparation Conditions

Different nanocrystalline magnesias were synthesized by precipitation and hydrothermal treatments of aqueous salt solutions in an attempt to tune their surface basicity. CO(2) was chosen as an acidic molecule to probe the basic sites by both temperature-programmed desorption and infrared spectroscopy. All samples were shown to be crystalline, and except that obtained by nitrate decomposition, they all possessed high surface areas. The oxides presented different basic site distributions, evidencing the significant role of the preparation conditions on tuning the surface basicity: while medium-strength basic centers are dominant in the samples prepared by precipitation aging or hydrothermal treatment, the one obtained by precipitation features a roughly equal concentration of medium-strength and strong centers. Infrared spectra revealed that hydrogen carbonate and monodentate and bidentate carbonates were formed in distinct proportion on all oxides. However, the bidentate complexes were shown to have different thermal stabilities; the more stable species are thought to be formed on acid-base pair centers associated with an anionic vacancy. Distinct morphological and structural characteristics were also observed by high-resolution transmission electron microscopy. It was consistently found that the high-surface area samples are formed by aggregates of nanoparticles (2-5 nm) randomly oriented and with a high concentration of structural defects. These findings allowed us to conclude that the surface heterogeneity promoted during synthesis increases the concentration of basic sites and plays an important role in tuning the basicity of the solids.

Preparation of carbon fiber/ZnO core-shell structure by a simple method

Carbon fiber/ZnO was prepared by surface modification precipitation in aqueous solution. Corresponding nucleation and crystal growth model was proposed for this structure. The effects of annealing temperature on the structure and absorptive properties of the composites were investigated. Results showed that obtained ZnO shell was ca. 200 nm on the surface of carbon fiber. The ZnO coating can protect the CFs from oxidation at a relatively high temperature. Energy bandgap calculated from the absorptive spectra was about 3.30 eV.

Formation of Magnesium Fluoride Particles of Different Morphologies

Uniform dispersions of magnesium fluoride particles of different morphologies were prepared by precipitation in aqueous solutions. The resulting cubic, prismatic, and platelet-like nanosize solids had single crystal structure with X-ray pattern characteristic of the mineral sellaite. In contrast, two kinds of polycrystalline MgF2 spheres were obtained by aggregation of the nanosize subunits. The mechanisms of the formation of the resulting particles of different shapes are explained by the role of the pH and ionic strength. In addition, for prospective numerical modeling the surface tension of spherical and platelet particles of MgF2 was evaluated from the X-ray data by a lattice parameter change method.

A Study on Corrosion Inhibitor for Magnesium Alloy

With the aim of evaluating corrosion inhibition for various inhibitors, a new qualitative method for corrosion inhibition effect test for magnesium and magnesium alloys was developed. The change of polarization current density of AZ61 magnesium alloy in electrochemical polarization experiments in alkali aqueous solution with 5mmol/L sodium dodecylsulphate(SDS), phytic acid(PA), ethylenediamine tetraacetic acid(EDTA), p-nitro-benzene-azo-resorcinol(PNBAR), acidum tannicum(AT) or stearic acid(SA) were tested. The SEM-EDS techniques and deposition experiment method were used for further confirmation of the corrosion inhibition. The results showed that those organic compounds which could form the inhibitor-magnesium precipitation in aqueous solution could be used as corrosion inhibitors for magnesium alloys to inhibit the increase of polarization current density as well as the dissolution and oxidation of magnesium alloys effectively.

Kinetics of iron(III) hydrolysis and precipitation in aqueous glycine solutions assessed by voltammetry

The kinetics of iron(III) hydrolysis and precipitation in aqueous glycine solutions were studied by cathodic voltammetry with a mercury drop electrode. The kinetics was controlled by changing ionic strength (I), pH and glycine concentration. Voltammetric measurements clearly showed formation and dissociation of a soluble Fe(III)–glycine complex, formation of iron(III) hydroxide and its precipitation. The rate constants of iron(III) hydroxide precipitation were assessed. The precipitation is first-order with respect to dissolved inorganic iron(III). The calculated rate constants of iron(III) precipitation varied from 0.18 × 10–5 s–1 (at 0.2 M total glycine, pH 7.30, I = 0.6 mol dm–3) to 2.22 × 10–3 s–1 (at 0.1 M total glycine, pH 7.30, I = 0.2 mol dm–3). At 0.5 M total glycine and I = 0.6 mol dm–3, the iron(III) precipitation was not observed.

Nanocrystal synthesis in an amphibious bath: spontaneous generation of hydrophilic and hydrophobic surface coatings.

Nanocrystalline materials are of intense and widespread interest because of their promising applications in biological labeling, chemical catalysis, micro/nanoelectronics, and energy production.[1] On the nanometer scale, semiconductors show size-dependent photoluminescence;[2] metals exhibit tunable surface plasmon bands;[1a,b] magnetic materials become superparamagnetic;[3] and chemical catalysts become more active.[1c,4] Recent research has led to high-quality and monodispersed colloidal nanocrystals by using a number of synthetic methods including reactions in reverse micelles,[5] arrested precipitation in aqueous solution,[5a,6] and organic-phase high temperature syntheses using hydrophobic coordinating ligands.[2a,7] The nanocrystals synthesized by these methods have shown various degrees of crystallinity, monodispersity, size-tunability, stability, and processibility. However, a major limitation is that the resulting nanoparticles are soluble only in the reaction solution or in chemically similar media.[8] For example, nanocrystals synthesized in trioctylphosphine oxide or other organic solvents are only soluble in nonaqueous media, whereas nanocrystals prepared in aqueous solution are not compatible with nonpolar solvents that are often used for fabrication of composite materials, device incorporation, and catalytic reactions.[9]

Rapid synthesis of submicron crystalline barium zirconate BaZrO 3 by precipitation in aqueous basic solution below 100 °C

Pure crystalline BaZrO 3 powders can be produced by precipitation in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH − concentration ([NaOH] = 20 mol/l), it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature (∼80 °C), after a short reaction time (15 min) and without requiring any precaution to avoid the presence of CO 2. This synthesis method yields spherical particles, whose size can be controlled by changing the concentration of the Ba + Zr solution. No calcination treatment is necessary since the precipitate is crystalline. Suitable choice of the synthesis parameters ([NaOH] = 20 mol/l, [Ba + Zr] = 1 mol/l, reaction time = 15 min) yields a sub-micron precipitate with excellent densification behaviour. Corrosion tests in BaO–CuO melt show that ∼98% dense BaZrO 3 obtained by sintering at 1650 °C for 13 h could be used for crucibles in the synthesis of YBa 2Cu 3O 7 superconducting single crystals.

Synthesis of Nanostructured Hydroxyapatite: A Comparative Study between Sol-Gel and Aqueous Solution Precipitation

Particle size is one of the most important factors to the successful application of calcium phosphate bioceramics as it may have an important role on its final properties such as mechanical resistance and reactivity. Thus, a process which results on very small and homogeneous particles is required, since it avoids further contamination derived from long milling times. On this context, a process such as sol-gel synthesis may be feasible, due to its simplicity on handling and its well known characteristic of producing homogeneous nanoparticles. Moreover, precipitated HA also may lead to satisfactory results regarding particle size and phase purity. The aim of this article was to demonstrate a preliminary characterization study of powders obtained by both methods and to compare them to a commercial sample available in Brazil. Characterization was made by XRD, Scherrer’s equation, XRF, SEM-LV, SEM-FEG and SEM-EDS. It has been found out that all samples consist of pure nanostructured hydroxyapatite with crystallite size between 37nm and 62nm.