Controlled Double-jet Precipitation Research Articles

Spectroscopic Study of Five-Coordinated Thermal Treated Alumina Formation: FTIR and NMR Applying.

This work represents research into materials designed to improve the environment. The study was carried out on aluminum hydroxide xerogels and alumina catalysts obtained by the Controlled Double Jet Precipitation (CDJP) process at different pH values. It has been shown that the pH of the CDJP process determines the content of aluminum-bound nitrate ions in the aluminum hydroxide. These ions are removed at a higher temperature than the decomposition of ammonium nitrate. The high content of aluminum-bound nitrate ions determines the structural disorder of the alumina and the high content of the penta-coordinated alumina catalyst.

A new approach for the synthesis of monodisperse zirconia powders with controlled particle size

In this work, the synthesis of hydrous zirconia by controlled double-jet precipitation (CDJP) was carried out in the pH range from 3 to 8. The evolution of particle shape and size during precipitation was investigated. It was found that at pH 3, 7, and 8 during the precipitation process there is no significant change in particle size, the suspension was gel-like, particles actively aggregated during drying. A gradual increase in particle size and a decrease in particle size dispersion specific for layer-by-layer aggregation was observed during CDJP at pH 4 to 6. The resulting particles do not aggregate and retain a rounded globular shape with a narrow size distribution during drying. Samples obtained at a pH above 6 are characterized after drying by a high specific surface area and porosity, as well as a reduced content of NO3- ions. The effect of pH precipitation on the phase composition and crystallite size of calcined samples was discussed.

Structural characterization and photoluminescence of (Gd1-xErx)2O3 nanophosphors synthesized by co-precipitation of layered precursors

In this paper, the layered (Gd1-xErx)2(OH)5NO3·nH2O (LGEH) with a variable content of erbium were synthesized by controlled double-jet precipitation (CDJP) at a constant pH value. The effect of pH co-precipitation on the morphology, crystallinity, porosity of the LGEH, as well as on the spectral-luminescent properties of oxide nanophosphors obtained by their heat treatment is significant. We have found that the samples with the lowest disordering and the highest of photoluminescence (PL) intensity of Er3+ ions are obtained from amorphous sponge-like precursor co-precipitated at pH 9.5. The PL of nanostructural (Gd1-xErx)2O3 depends on both structural-morphology properties and samples composition. It was also found that efficiency of radiative and non-radiative relaxation channels for excited Er3+ ions mainly depends on three factors: nanocrystals size, specific surface area and erbium concentration. For explanation of the PL behavior in the green and red spectral ranges, the energy diagram showing the intracenter energy transitions and intercenter energy migration in synthesized nanophosphors was proposed.

Evolution of layered yttrium hydroxide nitrate particles during controlled double-jet precipitation

Layered yttrium hydroxide nitrate particles Y2(OH)5(NO3)·xH2O (LYH) were synthesized by controlled double-jet precipitation (CDJP) in the pH range of 7–9.5. The pH value and the duration of precipitation, have a significant effect on the morphology and growth behavior of LYH particles. Spheroidal particles with a radial arrangement of straight polycrystalline plates were prepared at pH 7. The alignment and ordering of crystallites decreases at pH 8, which leads to the growth of many branching sheets that form huge spheroidal networks of LYH particles. During precipitation at pH > 8, irregularly shaped LYH agglomerates continuously form with a wide range of sizes. An assumption has been put forward about the decisive role of the two-step mechanism of nucleation/crystallization of LYH. The results of the study provide a simple way to prepare uniform spheroidal LYH particles promising for the production of functional oxide powders and ceramics.

Formation of high crystalline LDH sludge for removing Cu and Zn from wastewater by controlled double-jet precipitation.

In order to improve the heavy metal wastewater treatment by avoiding formation of amorphous sludge phase, we develop a faster formation of high crystalline layered double hydroxide (LDH) sludge to remove Cu and Zn from wastewater by controlled double-jet precipitation (CDJP) without hydrothermal or heat aging post-treatment. A series of experimental procedures are conducted to determine the optimal parameters. Results show that the optimal adding rate, pH value, and stirring rate is 0.5mLmin-1, 9.0, and 500rpm, respectively. The CuZnAl-LDH phase sludge is formed in a well-crystallized hexagonal platelet, which assembled into a flower-like architecture. Comparative studies show that the formation of amorphous LDH sludge in conventional precipitation (CP) could be divided roughly into two stages-from the mixed copper hydroxide, zinc hydroxide, and scarbroite to the mixed low crystallinity CuAl-LDH and ZnAl-LDH. However, in CDJP method, the high crystalline LDH sludge evolved from a new four-step evolution process that is the formation of an amorphous (quasi-)multinary metastable ternary CuZnAl-LDH phase, followed by the indiffusion of cations and substitution of anions to fabricate crystalline LDH, the integrated LDH hexagonal platelets assembled into a flower-like architecture by the screw dislocation growth mechanism, the coarsening growth of each ternary LDH platelet, respectively. Thereinto, the formation of (quasi-)multinary metastable LDH phase instead of metal hydroxide in initial stage would be an obvious advantage of the CDJP method compared to CP method due to the former skipping the sequential precipitation.

Facile synthesis of Fe3O4@Cu(OH)2 composites and their arsenic adsorption application

A directly coating method, controlled double-jet precipitation (CDJP), was developed for synthesizing magnetic Fe3O4@Cu(OH)2 composites in combination of advantages of magnetic rapid separation and satisfactory adsorption performance. The morphology and structure of the composites were analyzed by SEM, TEM, XRD, FTIR, XPS and VSM techniques. Through controlling the reaction on Fe3O4 particles, directly coating of Cu(OH)2 was successfully realized without the extra complicated procedures. The obtained Fe3O4@Cu(OH)2 consists of micro particles of size around 250nm coated with special leaflike nanomorphologies, possessing high saturation magnetization (from 56.5 to 98.84emug−1). As the amount of loaded Cu increased, As(V) removal of the composites augmented from 11.11 to 35.71mgg−1 far beyond that of reported traditional magnetic adsorbents. The adsorption isotherm was best fitted by Langmuir adsorption mode and the mechanism was mainly ascribed to the OH functionality of the Fe3O4@Cu(OH)2 composites and electrostatic attraction between As(V) species and Fe3O4@Cu(OH)2 composites. The Fe3O4@Cu(OH)2 composites is a promising candidate for treating arsenic contaminated water.

Chemical precipitation granular sludge (CPGS) formation for copper removal from wastewater

Solid–liquid separation and the settleability of sludge are always issues in copper wastewater treatment by chemical precipitation. To improve the settling performance of chemical precipitation sludge, controlled double-jet precipitation (CDJP) was used to treat wastewater by generating chemical precipitation granular sludge (CPGS). Several parameters such as the pH, copper oxide (CuO) seed dosage, stirring rate, adding rate and polyacrylamide dosage affecting the formation of the CPGS and wastewater treatment were investigated. Results show that the Cu(II) removal efficiency is over 99% and the settling velocity of the CPGS can reach up to 8.1 cm s−1 under optimized conditions, i.e., pH of 11, seed type of common CuO, seed dosage of 2.5 g L−1, stirring rate of 600 rpm, adding rate of 0.5 mL min−1 and PAM dosage of 20 g L−1. This settling velocity was about 18 times higher than that of chemical flocculent sludge. More importantly, the CPGS formation mechanism was explored. A three-step formation mechanism was proposed involving fresh precipitate growth on the seed surface, flocculation, and rearrangement with stirring.

Multifunctional nanocomposites for paper conservation

Upon aging, paper documents and books become progressively damaged. Paper deacidification is a fundamental conservation intervention. In this study, we report on the use of nanoparticles of titanium dioxide (TiO2) and magnesium hydroxide (Mg(OH)2) associated with hydroxyethylcellulose (HEC) to inhibit acidification, photo-induced degradation, and biodeterioration of paper. With the aid of ultrasound, Mg(OH)2 nanoparticles with a narrow size distribution can be obtained through homogeneous precipitation in water. Furthermore, to demonstrate the efficacy of the nanocomposite and the performance of treated and untreated paper, photo- and thermal-induced degradation is discussed. The results show that using the controlled double-jet precipitation (CDJP) it is possible to synthesize Mg(OH)2 particles with a narrow size distribution (18–87 nm). The nanocomposite of Mg(OH)2–TiO2–HEC increases the durability of paper by imparting fungal growth resistance (D = 34.6 mm), moderate alkalinity (pH = 8.4), mechanical reinforcement (from 817–896 N/m), and UV protection. Additionally, there is a slight color difference (ΔE* = 0.8) between the treated and untreated paper. Both photodegradation and thermal degradation indicate that the paper treated with this nanocomposite (Mg(OH)2–TiO2–HEC) has increased stability.

Potentiometric Determination of the Critical Supersaturation Ratio of Monodisperse Silver Chloride Grains in the Controlled Double-Jet Precipitation

Potentiometric Determination of the Critical Supersaturation Ratio of Monodisperse Silver Chloride Grains in the Controlled Double-Jet Precipitation

Rapid preparation of uniform colloidal indium hydroxide by the controlled double-jet precipitation

The synthesis of uniform colloidal rod-like In(OH)3 particles from relatively concentrated solutions of InCl3 (0.1 mol dm-3) in short reaction time (<15 min) by the controlled double-jet precipitation (CDJP) technique is described. The effects of the molar ratio of [NH4OH]/[InCl3], temperature, concentration of the reactants, and reaction time on the size and shape of the final products are investigated. It is found that such In(OH)3 particles are formed by aggregation of nanosize subunits.

Preparation and properties of uniform amorphous and crystalline colloidal nickel sulfide

Amorphous spherical particles of nickel sulfide of 10 nm in diameter were synthesized by the controlled double-jet precipitation (CDJP) technique using nickel sulfate and sodium sulfide. Cubic crystalline particles of 200 nm were obtained by aging dispersions of amorphous particles at 80 °C for more than a week, as long as the pH was kept between 3 and 3.5. Electrokinetic mobilities of these particles are reported, as well as color properties of their dispersions in liquids and in poly(vinyl alcohol) films are described.

Preparation and Growth Mechanism of Uniform Colloidal Copper Oxide by the Controlled Double-Jet Precipitation

Monodispersed crystalline CuO particles of different morphologies were synthesized by the controlled double-jet precipitation (CDJP) technique using NaOH and Cu(NO3)2as the reactants. The effects of temperature, reaction time, pH, and the concentrations of chemicals on the characteristics of final products were investigated. With lower [NaOH]/[Cu(NO3)2] molar ratios and temperatures, colloidal gerhardtite Cu2(OH)3NO3precipitated, while tenorite CuO particles of various morphologies were obtained at higher temperatures and [NaOH]/[Cu(NO3)2] ratios. Time resolved electron microscopy indicated that nanosized primary particles formed immediately after mixing the reactants, followed by aggregation into larger uniform particles of submicrometer size.

Controlled double-jet precipitation of uniform colloidal crystalline particles of Zr- and Sr-doped barium titanates

The synthesis of uniform colloidal crystalline particles of Zr- and Sr-doped barium titanates at a low temperature of 85 °C by the controlled double-jet precipitation (CDJP) technique is described. The stoichiometry of the powders can be precisely controlled by adjusting the compositions of the starting reactant solutions. Barium titanate with 20% Zr substitution, sintered at 1275 °C, satisfied the requirements for the Y5V multilayer capacitors application. The grain sizes are uniform and small, ranging from 1 to 3 μm. Solids with an extremely sharp change in the dielectric constant as a function of temperature, which are suitable for thermal IR detectors application, can be obtained when both Sr and Zr are incorporated as dopants.

Preparation of well-defined colloidal barium titanate crystals by the controlled double-jet precipitation

A new method for the preparation of well-defined colloidal barium titanate (BaTiO3) crystals by the controlled double-jet precipitation (CDJP) technique is described. The process is extremely fast and requires a low temperature (&lt;100 °C). The reactants, barium and titanium salts, can be used in high concentrations and the yield is quantitative. The stoichiometry of the BaTiO3 particles can be controlled precisely and reproducibly. The effects of the composition of the reactant solutions, flow rates, reaction time, and the addition of polymers on the precipitation process were investigated. The BaTiO3 powders, produced by the CDJP technique, sinter to high density at a temperature as low as 1200 °C and exhibit a relative dielectric constant of 5000 at 20 °C, which is the highest value reported in the literature. The grain sizes of the sintered samples are small and uniform, ranging between 1 and 2 μm.

Preparation of Silver Doped High Temperature Superconductors by the Controlled Double-Jet Precipitation

Chemical precursors of high temperature superconductors were prepared by the controlled double-jet precipitation of their oxalates to obtain suspensions with submicron average crystal size, narrow crystal size distribution, desired chemical composition and internal structure. To improve mechanical and electrical properties of HTSC layers the chemical precursors of HTSC were doped by silver oxalates using the same method. This technique enables to achieve better mixing of reagents in compare with mixed oxide processing. The suspensions were coagulated, washed and coated on various substrates. During carefully controlled heat treatment the grains readily sintered and formed HTSC layers. The layers prepared by this technique showed some improvements in mechanical and electrical properties. When coated on silver substrate, high density layer and a strong bond between the HTSC layer and substrate were achieved