Precipitation In Aqueous Solution Research Articles

A Comparative Study between β-TCP Prepared by Solid State Reaction and by Aqueous Solution Precipitation: Application in Cements

It is well known that calcium phosphate compounds are widely used as bone substitute due to their biocompatibility and bioactivity. Furthermore, recent studies have shown that slight changes in morphology or crystal structure can lead to several in vivo behaviours. Therefore, the purpose of this study was to investigate two different β-TCP synthesis routes (solid state reaction and aqueous solution precipitation) and their consequences on the final cement properties. It was found out that both routes are equivalent as there were no significant differences on their cement properties, except for mechanical resistance. The latter difference can also be attributed to the difference on the particle size distributions of the obtained β-TCP. These facts indicate that solid state reaction route is more interesting given its simplicity and yield.

Synthesis and spectral properties of starch capped CdS nanoparticles in aqueous solution

Synthesis of cadmium sulphide nanoparticles has been carried out in aqueous solution precipitation. Starch added during the synthesis of the nanoparticles resulted in cadmium-rich nanoparticles forming a stable complex with starch. The morphology and crystalline structure of such structures were measured by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD), respectively. The grain size of the nanoparticles determined by these techniques was of the order of 5 nm, which correlates well with measurements performed by Raman scattering and photoacoustic spectroscopy.

Reconciling kinetic and equilibrium observations of iron(III) solubility in aqueous solutions with a polymer-based model

Due to hydrolysis reactions, iron(III) forms oxyhydroxide precipitates in natural waters that minimise its availability to living organisms. Thermodynamic studies have established equilibrium concentrations of dissolved iron at various pH values, however these studies offer no insight into the kinetics of iron(III) polymerisation and subsequent precipitation. In recent work, the kinetics of iron(III) precipitation and dissolution of the precipitate have been investigated, but there are apparent discrepancies between the equilibrium solubility of iron(III) calculated from the kinetic parameters and its solubility measured by separation of the solid and dissolved phases at equilibrium. In this work, we reconcile kinetic and thermodynamic measurements using a polymer-based mechanistic model of the processes responsible for iron(III) precipitation in aqueous solutions based on a variety of previously published experimental data. This model is used to explain the existence of a solubility limit, including the effect of precipitate ageing on its solubility. We suggest that the model provides a unified approach for examining aqueous systems containing dissolved, solid-phase and surface species.

Study of effects of Mn 2+ in CdS nanocrystals

Mn 2+-doped CdS nanocrystals have been synthesized by adopting an aqueous solution precipitation method. These nanocrystals have been studied using X-ray diffraction (XRD), X-ray fluorescence (XRF), optical absorbance, photoluminescence (PL), DC electrical conductivity measurements and positron annihilation lifetime spectroscopy (PALS). The system has been found to be in the hexagonal phase. PL spectra have been studied on most prominent exciton peaks within the wavelength range (586–731 nm). The emission intensity is found to increase on increasing Mn 2+ ion concentration (0–5%). Electrical conductivity lies within 0.819×10 −6 to 1.69×10 −6 Ω −1 m −1 and the system shows power law dependence for n=3–3.77. The Cd vacancies concentration has been found to decrease on increasing Mn%.

FASTDXL: A Generalized Screen to Trap Disulfide-Stabilized Complexes for Use in Structural Studies

Structural studies of macromolecular complexes have produced extraordinary insights into a wide variety of biological processes. Unfortunately, as structural biologists pursue larger and more challenging assemblies, weakly stable and/or nonspecific interactions can become significant roadblocks to structure determination. We have developed a rapid and effective pool-based screen, termed FASTDXL (focused array screening technique for disulfide X-linking), to produce and identify disulfide-stabilized protein-nucleic acid assemblies. A significant strength of FASTDXL is that it can take advantage of prior structural knowledge about molecular interactions, but does not necessarily rely upon it. A detailed application of the approach to the difficult problem of trapping a bacterial primase-ssDNA complex is described, validating the method as a route toward obtaining diffracting crystals suitable for structure determination.

Study of C 6+ (80 MeV) ion induced effects on CdS:Mn system

Manganese-doped CdS nanocrystals have been synthesized by using aqueous solution precipitation method. These samples of CdS:Mn have been subjected to irradiation using C 6+ (80 MeV) under fluence of 1 × 10 13 ions/cm 2. For characterization X-ray diffraction (XRD), optical absorption, photoluminescence (PL), surface morphology and positron annihilation spectroscopy (PALS) have been performed. The system has been found in hexagonal phase having crystalline size distribution of 18–20 nm. The PL intensity has been found to be decreased, while optical band gap has been found to be increased of irradiated samples. Positron lifetime component τ 1 (210–183 ps) is due to annihilation from diffused vacancies on the grain surfaces and τ 2 (399–367 ps) is due to positrons directly trapped in the vacancy cluster like defects. The third component τ 3 (2453–2064 ps) is due to annihilation of orthopositronium, at interfaces and boundaries within the nanocrystals.

Photoluminescence of nanocrystalline SrMgF 4 prepared by a solution chemical route

SrMgF 4 was prepared by precipitation in aqueous solution. Alkaline earth metal acetates and ammonium fluoride were used as precursors. After drying and annealing the samples at different temperatures and times, single phase SrMgF 4 was obtained. By varying the annealing conditions, the mean crystallite size could be adjusted. Furthermore, the thermally treated samples displayed UV-excited intensive broad band luminescence in the visible region. The emissions colour and intensity can be adjusted by the tempering conditions. X-Ray diffraction, TEM-microscopy, fluorescence and IR-spectroscopy were used for analysis.

Synthesis of pure tetragonal zirconium oxide with high surface area

Zirconium oxide (ZrO2) with high surface area and high content of the tetragonal polymorph was prepared by precipitation from aqueous solutions under basic conditions in the presence of hexadecyltrimethylammonium bromide as surfactant. The surfactant to zirconium molar ratio, pH of precipitation, aging time and zirconium concentration in aqueous solution were optimized by the Taguchi method. The sample, prepared under optimized conditions had a high surface area of 168 m2 g−1 after calcination at 600 °C for 10 h. Pellets, prepared by pressing this sample and after calcination at 800 °C for 0.5 h had a surface area of 105 m2 g−1. X-ray diffraction analyses showed that both heat treatments gave pure tetragonal zirconium oxide.

Structural, optical, electrical and positron annihilation studies of CdS:Fe system

Nanocrystals of Cd 1− x Fe x S ( x = 0–0.05) have been synthesized by aqueous solution precipitation method at room temperature. The effect of doping of Fe 2+ ions (0–0.05) on CdS compound semiconductor has been studied, using X-ray diffraction (XRD), optical absorption (UV–vis), photoluminescence (PL), and positron annihilation spectroscopy (PAS). The structure of these nanocrystals is found to be single phase hexagonal. Optical absorption is found to be decreased on increasing the Fe 2+ ions concentration. PL spectra are studied on most prominent excitation peaks within the wavelength range (586–731 nm). The emission intensities are found to be decreased on increasing Fe 2+ ions concentration. DC electrical conductivity is found to be increased on increasing Fe 2+ ions at room temperature. The Cd vacancy concentration decreases with increasing Fe concentration.

Synthesis and luminescence properties of manganese-doped ZnS nanocrystals

Mn2+ doped ZnS nanocrystals were synthesized via aqueous solution precipitation method. The crystal structure of these nanocrystals is found to be cubic. The particle size of as prepared ZnS and (ZnS) Mn2+ was found in between the range of 4–6nm. The optical and photoluminescence studies of Zn1−xMnxS (x=0–5%) have also been performed at room temperature. The absorption and emission intensities were found to be increased on increasing Mn2+ concentration (0–5atom%). The Mn doped ZnS nanocrystals result blue shifted.

Synthesis of spherical metal oxide particles using homogeneous precipitation of aqueous solutions of metal sulfates with urea

Spherical micron sized porous particles of goethite FeO(OH), boehmite AlO(OH), anatase TiO 2, Zn(OH) 2 and binary mixtures of these oxides have been synthesized by homogeneous precipitation from aqueous solution containing urea in the presence of corresponding metal sulfates. Metal (hydrous) oxide particles obtained show spherical morphology and consist of agglomerated randomly oriented nanocrystallites. Synthesized metal oxide hydroxides were characterized using Brunauer–Emmett–Teller (BET) surface area and Barrett–Joiner–Halenda porosity (BJH), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX).

Morphology of aluminum phosphate by the Al-EDTA mediated particle formation in aqueous solutions at high temperatures

The morphology of aluminum phosphate, formed by homogeneous precipitation in aqueous solutions using Al-ethylenediaminetetraacetic acid (Al-EDTA) complex in the presence of H 2O 2, was investigated under several temperature conditions, and pH, Al-EDTA, and H 2O 2 concentrations. Spherical particles of AlPO 4· xH 2O ( x = 1.04–1.90) were formed at pH 4–8 at 125–200 °C. Since nonspherical precipitates were observed in the absence of EDTA or H 2O 2, the formation of the spherical particles at pH 4–8 is attributed to the slow release of Al 3+ ions by the degradation and/or dissociation of Al-EDTA with H 2O 2 under hydrothermal conditions. The size of the spherical particles obtained with Al-EDTA depends on the concentration of the Al-EDTA chelate and H 2O 2, and also on temperature; the size distribution of the particles decreased significantly with the H 2O 2 concentration and temperature.

Thermally Induced Phase Transition of Carborane-Functionalized Aliphatic Polyester Dendrimers in Aqueous Media

Three recently reported aliphatic polyester dendrimers of generations 3, 4, and 5, having 4, 8, and 16 carborane cages within their interior, respectively, were found to exhibit thermally induced, reversible precipitation in aqueous solution. The cloud-point temperatures for these molecules were observed to be between 40 and 80 degrees C, depending on the dendrimer generation. The three dendrimers investigated have a hydroxyl-to-carborane ratio of 8:1, which provides the ideal balance between the hydrophobic interior and the hydrophilic exterior to enable the thermally induced phase transition to occur. It was found that repeated heating/cooling cycles resulted in a decreasing cloud-point temperature and increased dendrimer solubility. Additionally, the effect of pH on the cloud point was investigated, indicating no significant changes as long as the dendrimers remained stable. Size-exclusion chromatography indicated that dendrimer degradation was occurring at pH above 7.0.

Off‐resonance Raman spectroscopy of Cd1–xMnxS nanoparticles

AbstractCd1–xMnxS nanoparticles (NPs) with average radius Ro = 2.2 nm have been investigated by Raman scattering measurements. The nanoparticles, synthesized using aqueous solution precipitation, are small enough to show effects due to confinement. The dominant line was at about 300 cm–1 having asymmetric broadening for ω < 300 cm–1. Significant change in intensity for different x and excitation energies was noticed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A new method for the study of trace element partitioning between calcium carbonate and aqueous solution: A test case for Sr and Ba incorporation into calcite

A new experimental method (evaporation method) for calcium carbonate precipitation in aqueous solution was attempted in order to develop a convenient and controllable experimental technique for obtaining precise trace element partition coefficients. Calcite crystals were formed by evaporation of H2O from the aqueous mother solution using a dehumidifier, and the consumed Ca ions were supplied from a refill solution to maintain supersaturation. This method has been tested for Sr and Ba partition coefficients using NaCl (3.5%) solution under room temperature and pressure. The results of two runs give Sr partition coefficients of 0.0585 and 0.0546, and Ba partition coefficients of 0.0302 and 0.0275 for growth rates of 152 and 499 μmol · m-2 · hr-1, respectively. It was found that this method has several merits for partitioning experiments: (1) pH of the solution is close to the natural ones, for example, pH of 8.08 in the present case is close to that of seawater; (2) chemical composition of the mother solution can be chosen to imitate natural composition; (3) the crystal growth rate is controllable in a relatively small range and is measurable; and (4) temperature and PCO2 pressure can be controlled. The relative errors of the partition coefficients in the present study were estimated to be about 5%. The results seem to be promising, and suggest that more precise determination of partition coefficients could be possible via more careful experimental handling and improving the apparatus.

Kinetics of Fe(III) precipitation in aqueous solutions at pH 6.0–9.5 and 25 °C

The kinetics of Fe(III) precipitation in synthetic buffered waters have been investigated over the pH range 6.0–9.5 using a combination of visible spectrophotometry, 55Fe radiometry combined with ion-pair solvent extraction of chelated iron and numerical modeling. The rate of precipitation, which is first order with respect to both dissolved and total inorganic ferric species, varies by nearly two orders of magnitude with a maximum rate constant of 16 ± 1.5 × 10 6 M −1 s −1 at a pH of around 8.0. Our results support the existence of the dissolved neutral species, Fe(OH) 3 0, and suggest that it is the dominant precursor in Fe(III) polymerization and subsequent precipitation at circumneutral pH. The intrinsic rate constant of precipitation of Fe(OH) 3 0 was calculated to be k Fe ( OH ) 3 0 = 2.0 × 10 7 M - 1 s - 1 allowing us to predict rates of Fe(III) precipitation in the pH range 6.0–9.5. The value of this rate constant, and the variation in the precipitation rate constant over the pH range considered, are consistent with a mechanism in which the kinetics of iron precipitation are controlled by rates of water exchange in dissolved iron hydrolysis species.

Effect of Cu ion on the formation and magnetic properties of nanocrystalline magnetite prepared in an aqueous solution

We prepared the nanocrystalline magnetite from precipitation in aqueous solution varying the concentration of Cu/sup 2+/ ion. The magnetite powder prepared at the Fe/sup 2+//Cu/sup 2+/ mole ratio=1:0.5 exhibited that its Cu content was about 5.4 wt% and its particle size was about 20 nm. A Mo/spl uml/ssbauer study showed that Cu ions were disordered in both the A and B sites. With the higher Fe/sup 2+//Cu/sup 2+/ mole ratio, the particle size increased. At the Fe/sup 2+//Cu/sup 2+/ mole ratio below 0.5, superparamagnetic particles of a few nanometer in size appeared and lowered the saturation magnetization as well as the coercivity. These magnetic properties became maximized in the powder prepared at the Fe/sup 2+//Cu/sup 2+/ mole ratio of 0.5.

Preparation, structure and electrochemical performances of nanosized cathode active material Ni(OH) 2

Nanosized cathode material Ni(OH) 2 was prepared by aqueous solution precipitation reaction under ultrasonic dispersing condition. The Ni(OH) 2 products were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM). The electrochemical performances of the Ni(OH) 2 samples were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscope (EIS). The charge–discharge tests were conducted on the batteries with the sample as the positive electrode active material. The XRD and SEM results shows that nano-sized Ni(OH) 2 prepared in this study is beta-type crystal with the particle size range from 10–40nm with regular spherical shapes. The results from CV and EIS measurement indicate that the nano-sized Ni(OH) 2 exhibits excellent electrochemical performance, e.g., batter electrochemical reversibility and higher proton diffusion rate, smaller polarization and better discharge property than that of usual spherical Ni(OH) 2; and the measured apparent diffusion coefficiency of proton is 1.8 × 10 − 12 cm 2 s − 1 ; and the specific discharge capacity of the nano-sized Ni(OH) 2 electrode is 381 mAh/g.

Biliary cholesterol crystallization characterized by single-crystal cryogenic electron diffraction

Cholesterol crystals are the building blocks of cholesterol gallstones. The exact structure of early-forming crystals is still controversial. We combined cryogenic-temperature transmission electron microscopy with cryogenic-temperature electron diffraction to sequentially study crystal development and structure in nucleating model and native gallbladder biles. The growth and long-term stability of classic cholesterol monohydrate (ChM) crystals in native and model biles was determined. In solutions of model bile with low phospholipid-to-cholesterol ratio, electron diffraction provided direct proof of a novel transient polymorph that had an elongated habit and unit cell parameters differing from those of classic triclinic ChM. This crystal is exactly the monoclinic ChM phase described by Solomonov and coworkers (Biophysical J., In press) in cholesterol monolayers compressed on the air-water interface. We observed no evidence of anhydrous cholesterol crystallization in any of the biles studied. In conclusion, classic ChM is the predominant and stable form in native and model biles. However, under certain (low phospholipid) conditions, transient intermediate polymorphs may form. These findings, documenting single-crystal analysis in bulk solution, provide an experimental approach to investigating factors influencing biliary cholesterol crystal nucleation and growth as well as other processes of nucleation and crystallization in liquid systems.

Cd<sub>1-x</sub>Mn<sub>x</sub>S Nanoparticles: Far-Infrared Phonon Spectroscopy

Phonon spectra of Cd1-xMnxS (x = 0; 0.01; 0.05; 0.1; 0.15; 0.3) nanoparticles (d ~ 4.5 nm) have been investigated by far-infrared reflection (FIR) (spectral range 40 - 600 cm-1, temperature range 80 – 300 K) and Raman spectroscopy (100 – 700 cm-1, 300 K). Cd1-xMnxS nanoparticles have been synthesized by using aqueous solution precipitation. We obtained interesting features in FIR spectra: there are expected modes of bulk CdS (240 cm-1, 300 cm-1), new modes connected with nano-size of CdS (130 cm-1, 170 cm-1) and additional mode at 120 cm-1 in Cd1-xMnxS nanoparticles which can be assigned to the presence of Mn. The position of obtained modes is discussed in the frame of the linear chain model with both mass and force constant defects. Raman spectroscopy gives us only the mode at 300 cm-1 and its second harmonic.