Co-precipitation In Aqueous Media Research Articles

The roles of Co-precipitation pH, phase-purity and alloy formation for the ammonia decomposition activity of Ga-promoted Fe/MgO catalysts

A series of mesoporous MgFe1.75Ga0.25O4 mixed spinel oxides obtained upon calcination of hydrotalcite-like precursors was investigated in the ammonia decomposition reaction at 1atm after reduction in H2 atmosphere. The corresponding precursors were synthesized from metal salt solutions at five constant pH values in the range between 8.5 and 10.5 by co-precipitation in aqueous media to study the impact of pH variation on the catalyst’s structure and activity. N2 physisorption, thermogravimetric analysis, powder X-ray diffraction, Mössbauer spectroscopy, and temperature programmed techniques (H2-TPR and NH3-TPD) were applied to gather information about the textural, (micro-)structural, and adsorption properties of the samples. While phase purity in the precursor and oxide stages is only observed for pH=10, undesired by-phases (MgFe2O4 and/or Fe3O4) are additionally formed during co-precipitation at the remaining pH values. This is partly related to an incomplete precipitation of Mg2+ cations in less alkaline environments. In situ XRD measurements during reduction revealed that Fe-Ga alloys are formed between 500 and 600°C. The absence of by-phases avoids the formation of α-Fe, thus improving the structural and compositional homogeneity of the nitridated samples. This beneficial effect is reflected by the low activation energy (70kJ/mol) and the enhanced low temperature activity (<450°C) of the phase pure material in the catalytic decomposition of ammonia.

Comparative Photocatalytic Performance on the Degradation of 2-Naphthol Under Simulated Solar Light Using α-Bi4V2O11 Synthesized by Solid-State and Co-precipitation Methods

In this investigation, the photocatalytic activity of α-Bi4V2O11 in the degradation of 2-naphthol under simulated solar light was evaluated. Bismuth vanadate α-Bi4V2O11 was synthesized by the solid-state reaction method and by co-precipitation in aqueous media, with the aim of comparing their performance in the photodegradation of the aromatic pollutant. The latter method (co-precipitation) has not been previously reported for the synthesis of α-Bi4V2O11. Structural evolution of the oxides precursors was determined by X-ray diffraction. Morphology and optical properties of the solids were analyzed by scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectroscopy (UV-vis), respectively. The results showed that at 800 °C, only α-Bi4V2O11 was formed in both preparations. The SEM micrographs revealed that the powders were composed of agglomerates with sizes between 0.8–2 μm for those synthesized by co-precipitation and 2–10 μm for those obtained by solid-state reaction. The optical properties indicated that α-Bi4V2O11 was activated with visible light during the photocatalytic process. The photocatalytic degradation of 2-naphthol was largely influenced at basic pH, degrading 79% of the contaminant in 240 min, with the powder obtained by co-precipitation; meanwhile, for the solid-state preparation, the degradation reached only 55%.

Photoelectrochemical properties of FTO/p-NiO electrode induced by UV light irradiation

Photoelectrochemical properties of p-nickel oxide (NiO) thin film deposited on fluorine-doped tin oxide (FTO) electrode, by combination of co-precipitation in aqueous media along with the dip-coating process, were investigated by cyclic voltammetry and chronoamperometry techniques in sodium sulfate (Na2SO4) electrolyte solution. The electrochemical characterization measurements have shown that the FTO/p-NiO electrode presents sensitivity to UV light, as observed by the increased photo-induced current, exposed to a more negative potential. The photoelectrochemical parameters obtained were photocurrent response time (∆t1), photocurrent decay time (∆t0), and photocurrent density stability (jph, jlight on − jlight off). Besides, this electrode shows excellent performance for methylene blue degradation under UV light irradiation condition, with estimated kobs value of 170 × 10−4 min−1, which is nine times higher than the dark condition and about three times higher than NiO powder catalyst. Results presented here allow concluding that the p-NiO thin film stands as an important electrode material with technological potential to be used directly in environmental preservation.

SiO2-template synthesis of mesoporous MgF2 highly effective for Cl/F exchange reaction

An efficient and cost-effective route has been developed for the controllable synthesis of high-surface-area MgF2 materials with variable surface acidity and improved catalytic performance for Cl/F exchange reaction. This route is based on a facile non-surfactant template method, in which MgO–SiO2 precursors were obtained at varied Si/Mg ratios via ammonia coprecipitation in aqueous media, followed by depletion of the SiO2 template in 40% aqueous HF solution. The thus-derived MgF2 is featured with superior surface area, uniform mesopores, and significantly improved Lewis acidity relative to conventional MgF2. Among samples synthesized, that with Si/Mg molar ratio at 1/6 achieved the highest surface area amounted to 92m2/g after calcination at 573K. Probe reaction by CHClF2 dismutation has demonstrated far superior Cl/F exchange activities for SiO2-templated MgF2 samples relative to their non-templated analog, as may be accounted for by the combined effect of promoted surface properties and significantly enhanced surface acidity.

Colorimetric and microscopic study of the thermal behavior of new ceramic pigments

The article studies thermal resistance variation by analyzing the colorimetric parameters correlated with the optical microscopy data of two groups of ceramic pigments obtained by co-precipitation in aqueous medium of phosphate anion and of a mixture of chromium phosphate with various chromophore cations. This research enabled us to reveal the thermal thresholds/domains within which significant color changes occur, thus allowing the choice of pigments compatible with the thermal varnishing-glazing processes involved in the manufacture of tesserae for mosaic and stained glass and of colored materials for floor tiles, wall tiles and painted porcelain.

Deposition and photo-induced electrical resistivity of dip-coated NiO thin films from a precipitation process

Thin films of the semiconductor NiO are deposited using a straightforward combination of simple and versatile techniques: the co-precipitation in aqueous media along with the dip- coating process. The obtained material is characterized by gravimetric/differential thermal analysis (TG–DTA) and X-ray diffraction technique. TG curve shows 30 % of total mass loss, whereas DTA indicates the formation of the NiO phase about 578 K (305 °C). X-ray diffraction (XRD) data confirms the FCC crystalline phase of NiO, whose crystallinity increases with thermal annealing temperature. UV–Vis optical absorption measurements are carried out for films deposited on quartz substrate in order to avoid the masking of bandgap evaluation by substrate spectra overlapping. The evaluated bandgap is about 3.0 eV. Current–voltage (I–V) curves measured for different temperatures as well as the temperature-dependent resistivity data show typical semiconductor behavior with the resistivity increasing with the decreasing of temperature. The Arrhenius plot reveals a level 233 meV above the conduction band top, which was attributed to Ni2+ vacancy level, responsible for the p-type electrical nature of NiO, even in undoped samples. Light irradiation on the films leads to a remarkable behavior, because above bandgap light induced a resistivity increase, despite the electron–hole generation. This performance was associated with excitation of the Ni2+ vacancy level, due to the proximity between energy levels.

Polyglycerol‐grafted superparamagnetic iron oxide nanoparticles: highly efficient MRI contrast agent for liver and kidney imaging and potential scaffold for cellular and molecular imaging

Polyglycerol as a water-soluble and biocompatible hyperbranched polymer was covalently grafted on the surface of superparamagnetic iron oxide nanoparticles. With this aim, superparamagnetic magnetite nanoparticles were prepared by coprecipitation in aqueous media, then the surface of nanoparticles was modified to introduce the reactive groups on the surface of nanoparticles. After that, polyglycerol was grafted on the surface of nanoparticles by ring-opening anionic polymerization of glycidol using n-bulyllithium as initiator. The magnetometry, relaxometry and phantom MRI experiments of this highly stable ferrofluid showed its high potential as a negative MRI contrast agent. Calculated r(1) and r(2) relaxivities at different magnetic fields were higher than the values reported for commercially available iron oxide contrast agents. The in vivo MRI studies showed that, after intravenous injection into mice, the particles produced a strong negative contrast in liver and kidneys, which persisted for 80 min (in liver) to 110 min (in kidneys). The negative contrast of the liver and kidneys weakened over the time, suggesting that polyglycerol coating renders the nanoparticles stealth and possibly optimal for renal excretion.

Application of magnetic iron oxide nanoparticles prepared from microemulsions for protein purification

AbstractBACKGROUND: Magnetic nanoparticles are of immense interest for their applications in biotechnology. This paper reports the synthesis of magnetic iron oxide nanoparticles from two different water‐in‐oil microemulsion systems (ME‐MIONs), their characterization and also their use in purification of coagulant protein.RESULTS: ME‐MIONs have demonstrated to be an efficient binder in the purification of Moringa oleifera protein when compared with the superparamagnetic iron oxide nanoparticles prepared from coprecipitation in aqueous media. The size and morphology of the ME‐MIONs were studied by transmission electron microscopy (TEM) while the structural characteristics were studied by X‐ray diffraction (XRD). The microemulsion magnetic iron oxide nanoparticles (ME 1‐MION and ME 2‐MION) obtained have a size range 7–10 nm. The protein and ME‐MIONs interaction was investigated by Fourier transform infrared spectroscopy (FT‐IR); the presence of three peaks at 2970, 2910 and 2870 cm−1 respectively, confirms the binding of the protein. The purification and molecular weight of the coagulant protein was 6.5 kDa as analyzed by SDS‐PAGE.CONCLUSION: The ME‐MIONs have the advantage of being easily tailored in size, are highly efficient as well as magnetic, cost effective and versatile; they are, thus, very suitable for use in a novel purification technique for protein or biomolecules that possess similar characteristics to the Moringa oleifera coagulant protein. Copyright © 2011 Society of Chemical Industry

Effect of solvent-induced structural modifications on optical properties of CdS nanoparticles

We have investigated the effects of solvent used during synthesis on structural and optical properties of CdS quantum dots. Different methods of synthesis for the production of CdS quantum dots are presented. These are: (a) wet chemical co-precipitation in non-aqueous medium (i.e. methanol); (b) wet chemical co-precipitation in aqueous medium (deionized water) and (c) solid state reaction. It is demonstrated that the use of methanol as solvent leads to a strong enhancement of PL intensity of CdS quantum dots for use in optoelectronic devices. These products were characterized by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The change in bandgap with size-quantization was investigated by UV-VIS absorption spectroscopy. CdS nanocrystals prepared in non-aqueous medium have narrow size distribution than those prepared in aqueous medium and solid state reaction. Phase transformation of CdS nanocrystals from a cubic to hexagonal structure was observed in methanol solution. The formation of CdS/Cd(OH)2 nanostructure was also confirmed using X-ray diffraction pattern. This suggests that the strong enhancement of the PL intensity may have originated from the remarkable reduction of non-radiative recombination process, due to surface defects of quantum dots. The red shift of the Raman peaks compared to that for bulk CdS may be attributed to optical phonon confinement.

Visible-Light-Induced Photocatalyst Based on Nickel Titanate Nanoparticles

TiO2-coupled NiTiO3 nanoparticles have been prepared by coprecipitation in aqueous medium followed by sintering. Powder X-ray diffraction (PXRD) and high-resolution transmission electron microscopy (HRTEM) were used to characterize the crystalline structure. The crystalline sizes of both TiO2 and NiTiO3 were estimated to be in the range of 40−50 nm. A noticeable optical absorbance in the visible range was observed by UV−vis diffuse reflection spectroscopy (DRS). The photocatalytic activities were evaluated in the degradation of methylene blue in aqueous solution. The results show that the TiO2-coupled NiTiO3 nanoparticles exhibit good photocatalytic activities under visible light irradiation. The NiTiO3 phase was found to be indispensable for photoabsorption and photocatalysis.

The low temperature synthesis and characterization of Bi 3.25La 0.75Ti 3O 12 powder by hydroxide coprecipitation in aqueous medium

The fine powders of Bi 3.25La 0.75Ti 3O 12 (BLT) were prepared by coprecipitaton method in aqueous medium at low temperature. The differential thermal analysis (DTA), thermo-gravimetric analysis (TG) and X-ray diffraction (XRD) were employed to evaluate the phase formation of BLT and TEM was used to characterize and observe the particle size and morphology of BLT powder obtained. The results show that the bismuth layer perovskite phase of BLT can begin to form at as low as 500 °C by the coprecipitation method. When the precipitates obtained were calcined at 600 °C for 2 h, the mono-phase and perfect BLT powder was synthesized. The BLT powder obtained consists of irregular or plate-like particles which are less than about 100 nm and is nearly aggregate free.

Comparison between different LiFePO 4 synthesis routes and their influence on its physico-chemical properties

LiFePO 4 powders were synthesized under several different conditions (solid state reactions at high temperatures, co-precipitation in aqueous medium, hydrothermal synthesis or mechanochemical activation). The samples were characterized by X-ray diffraction (XRD), chemical titration and their electrochemical performance were investigated in terms of cycling behavior. We also report, in this work, the benefit of introducing an electronic conductor precursor (typically a sucrose) during or after the synthesis in order to overcome the poor charge transfer associated with the lithium iron phosphate.

Low temperature synthesis of lead zirconate titanate powder by hydroxide co-precipitation

A method to synthesize lead zirconate titanate (Pb(Zr 0.53Ti 0.47)O 3) by co-precipitation in aqueous medium is described. The as-prepared powders were heat-treated at 550 and 700 °C. DTA, TG and XRD were employed to follow and characterize the phase evolution. The results show that mono-phase, tetragonal Pb(Zr 0.53Ti 0.47)O 3 powder can be synthesized at considerably low temperature.

Role of MgO and Cr 2O 3 additives on the properties of zirconia–mullite composites

Precursor powder for zirconia–mullite composite was synthesized by co-precipitation in aqueous medium taking inorganic salts of aluminium, silicon and zirconium in requisite amounts. The powder was thoroughly characterized in terms of chemical composition, surface area, DTG behavior and FT–IR spectra. Role of two additives, namely, MgO and Cr 2O 3, on the densification of the compacted powder at different elevated temperatures ca. 1300–1500 °C was studied by the measurement of different physico-mechanical properties, such as bulk density, apparent porosity, specific gravity, compressive strength, bending strength and fracture toughness. Phase analysis by XRD technique and phase distribution by SEM technique was carried out to evaluate the microstructure of the sintered materials.

Thermal evolution crystal structure and cation valence of Mn in substituted Ba-β-Al2O3 prepared via coprecipitation in aqueous medium

BaMnxAl12−xO19−α combustion catalysts with x = 0.5, 1.0, 2.0, 3.0 have been prepared via coprecipitation in aqueous medium. Thermal evolution from 380 up to 1670 K has been followed by XRD and surface area measurements. The crystal structure of the final material and the dominant oxidation state of Mn in the different crystallographic sites, have been investigated by means of XANES spectroscopy and Rietveld refinements of diffraction powder data sets collected in proximity and far from the MnK absorption edge. It was found that, except for the highest Mn content (x = 3), monophasic samples are obtained upon calcination at 1470 K. For the whole compositional range the Ba-βI-Al2O3 structure is obtained. A formation mechanism involving Ba ion diffusion within the γ-Al2O3 spinel blocks, similar to that observed for Mn-free samples, is active also in this case. However, the presence of Mn ions favours the formation of the Ba-βI-Al2O3 that occurs at lower temperatures. At low Mn loading (up to x = 1), Mn preferentially enters the tetrahedral Al(2) sites of the Ba-βI-Al2O3 as Mn2+. At higher loading, Mn preferentially enters the octahedral Al(1) sites as Mn3+. A charge compensation mechanism, involving the occupancy of Ba sites in the mirror planes, operates to balance the substitution of Al3+ with Mn2+. The presence of Mn ions also affects the morphological properties of the final material.

Calcium-lead-copper and calcium-lead-cadmium hydroxylapatite solid solutions: Preparation, infrared and lattice constant measurements

Homogeneous solid solutions of Ca/Pb/Cu hydroxylapatites, keeping the Ca content fixed, and Ca/Pb/Cd hydroxylapatites, maintaining the Cd amount fixed, have been prepared over the entire Cu/Pb and Ca/Pb composition ranges respectively by the method of co-precipitation in aqueous media. I.r. frequencies and lattice constants of the solid solutions have been obtained and are found to vary linearly with composition.

Strontium-copper-calcium hydroxyapatite solid solutions: Preparation, infrared, and lattice constant measurements

Homogeneous solid solutions of strontium, copper, and calcium hydroxyapatite (Ca l Sr m Cu n ) 10(PO 4) 6 (OH) 2 with fixed n = 1 have been prepared over the entire compositional range by coprecipitation in aqueous media by the addition of ammonium dihydrogen phosphate to solutions of strontium, copper, and calcium nitrate made strongly basic with aqueous ammonia. The infrared spectra and lattice constants of the solid solutions have been measured and found to vary linearly with composition between those of the pure end members.

Preparation, IR, and lattice constant measurements of mixed (Ca + Cu + Zn) hydroxylapatites

Homogeneous solid solutions of calcium, copper, and zinc hydroxylapatites keeping zinc content fixed have been prepared over the entire compositional range by the method of coprecipitation in aqueous media. Frequencies (cm −1) and assignment for the infrared absorption and the lattice constants of the solid solutions have been measured and found to vary linearly with composition.

Mangnesium calcium hydroxylapatite solid solutions: Preparation, IR and lattice constant measurements

Homogeneous solid solutions of magnesium and calcium hydroxylapatite have been prepared over the entire compositional range by the method of co-precipitation in aqueous media. Frequencies (cm −1) and assignments for the IR absorption and the lattice constants of the solid solutions have been measured and found to vary linearly with composition between those of the pure end members.