Formation of NiFe2O4 nanoparticles by mechanochemical reaction

Preparation of nanosized NiFe₂O₄ particles by mechanochemical reaction(NiO+α-Fe₂O₃) and subsequent thermal treatment was investigated using X-ray diffraction (XRD). Thermal treatment of the as-milled powder at 700 °C for 1 h led to the formation of NiFe₂O₄ nanoparticles with an average crystal size of about 23 nm. Effect of thermal treatment temperature on the crystal size of the nanoparticles was studied. The mechanism of nanoparticles growth was primarily discussed. The activation energy of NiFe₂O₄ nanoparticle formation during calcination was calculated to be 16.6 kJ/mol.     

Hydrothermal synthesis, characterization, and influence factors of PbTe nanocrystals

In the present paper, we successfully prepared PbTe nanocrystals in a simple aqueous system via the hydrothermal route employing PbO, Te powders and N₂H₄·H₂O as the starting reactants at 150 °C for 14 h. Some factors affecting the morphologies of the PbTe nanocrystals, such as the reaction temperature, time, the amount of NaOH, sorts of reductants and Pb²⁺ ion sources, were systematically investigated. Experimental results indicated that, under keeping the other experimental conditions constant: raising the reaction temperature, the shapes of the as-obtained PbTe hardly changed, while decreasing the temperature, some PbTe dendrites were obtained; the short reaction time availed to obtain cubes with a hole in the center of each face; more amounts of NaOH were favorable to the formation of regular PbTe nanocuboids. When NaBH₄ was used as the reductant, a large amount of near spherical PbTe nanocrystals was produced; while NaH₂PO₂ was used, many PbTe crystals with hollow framework structures were obtained. When Pb(CH₃COO)₂ was used as the Pb²⁺ ion source, some dendrites made of many irregular particles were generated; while PbSO₄ was employed, many PbTe nanocuboids were produced. A possible formation mechanism of PbTe nanocrystals was proposed based on the experimental results.     

Microwave-assisted fast vapor-phase transport synthesis of MnAPO-5 molecular sieves

MnAPO-5 was prepared by a microwave-assisted vapor-phase transport method at 180 °C in short times. The products were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectra, UV-vis spectroscopic measurement, NH₃-temperature-programmed desorption and esterification reaction. It was found that dry gels prepared with aluminum isopropoxide, phosphoric acid and manganese acetate could be transferred to MnAPO-5 in the vapors of triethylamine and water by the microwave-assisted vapor-phase transport method at 180 °C for less than 30 min. The crystallization time was greatly reduced by the microwave heating compared with the conventional heating. The resulting MnAPO-5 exhibited much smaller particle sizes, higher surface areas and slightly higher catalytic activity in the esterification of acetic acid and butyl alcohol than those prepared by the conventional vapor-phase transport method and hydrothermal synthesis.     

Size-controlled synthesis of alumina nanoparticles from aluminum alkoxides

Aluminum oxide nanoparticles were prepared by the hydrolysis of aluminum oxide alkoxides followed by calcinations, in the presence of surface stabilizing agents, such as Na(AOT) molecules. The size of alumina precursors (bohemite) was 20-30 nm, yielding aluminum oxide particles with an average size of 80 nm after calcinations at 1200 °C. The shape of the α-alumina nanoparticles was mainly spherical and the high temperature inhibited the formation of the hexagonal crystals. The introduction of Na(AOT) during the appropriate processing step, had the effect of controlling the size of the particles, the degree of aggregation and the particles shapes.     

Size-controlled synthesis of ZrO2-TiO2 nanoparticles prepared via reverse micelle method: Investigation of particle size effect on the catalytic performance in vapor phase Beckmann rearrangement

Zirconium-titanium mixed oxide nanoparticles have been synthesized using microreactors made of bis-(2-ethylhexyl) sulfosuccinate (AOT)/water/n-hexane microemulsions. The control of particle size was achieved by varying the process variables, such as water-to-surfactant molar ratio and reagent concentration. Their sizes, appearances, crystal structures, pore diameter and surface area were characterized by TEM, XRD, N₂ adsorption/desorption methods. The results revealed that samples prepared in reverse micelles had no crystalline phase. The Beckmann rearrangement of cyclohexanone oxime on ZrO₂-TiO₂ nanoparticles was carried out in a fixed-bed down flow reactor to investigate the effect of particle size on catalytic activity and selectivity. Samples synthesized in reverse micelles had better reaction performance than samples prepared via sol-gel method. A parallel relationship could be drawn between the catalytic activity and the particle size as well as the selectivity of the catalyst.     

Electrochemical synthesis of calcium carbonate coatings on stainless steel substrates

Calcite CaCO₃ has been electrocrystallized on stainless steel substrates by the galvanostatic cathodic reduction of aqueous calcium bicarbonate solutions. The deposition is controlled by pH changes occurring close to the cathode due to electrogeneration of base. The deposit morphology varies from facetted rhombs observed at low (1-20 mA cm⁻²) current densities to corner-rounded particles observed at high (40 mA cm⁻²) current densities.     

Microwave-hydrothermal synthesis of perovskite bismuth ferrite nanoparticles

Hydrothermal microwave method (HTMW) was used to synthesize crystalline bismuth ferrite (BiFeO₃) nanoparticles (BFO) in the temperature of 180 °C with times ranging from 5 min to 1 h. BFO nanoparticles were characterized by means of X-ray analyses, FT-IR, Raman spectroscopy, TG-DTA and FE-SEM. X-ray diffraction results indicated that longer soaking time was benefit to refraining the formation of any impurity phases and growing BFO crystallites into almost single-phase perovskites. Typical FT-IR spectra for BFO nanoparticles presented well defined bands, indicating a substantial short-range order in the system. TG-DTA analyses confirmed the presence of lattice OH⁻ groups, commonly found in materials obtained by HTMW process. Compared with the conventional solid-state reaction process, submicron BFO crystallites with better homogeneity could be produced at the temperature as low as 180 °C. These results show that the HTMW synthesis route is rapid, cost effective, and could be used as an alternative to obtain BFO nanoparticles in the temperature of 180 °C for 1 h.     

A solvothermal synthesis of ultra-fine iron phosphide

Powder iron phosphide (FeP) has been prepared via a benzene-thermal synthesis with the reaction of anhydrous iron chloride (FeCl₃) and sodium phosphide (Na₃P) at 180-190°C. The product was analyzed by X-ray photoelectron spectroscopy (XPS), and the results show the mole ratio of Fe:P is 1.12. X-ray diffraction (XRD) pattern can be indexed to the orthorhombic cell of FeP with the lattice constant a=5.191, b=3.101, and c=5.789 Å. Transmission electron microscope (TEM) images indicate that average particle size is about 200 nm in diameter.     

IF-WS2 nanoparticles size design and synthesis via chemical reduction

An innovative synthesis of inorganic fullerene-like disulfide tungsten (IF-WS₂) nanoparticles was developed using a chemical reduction reaction in a horizontal quartz reactor. In this process, first tungsten trisulfide (WS₃) was formed via a chemical reaction of tetra thiotungstate ammonium ((NH₄)₂WS₄), polyethylene glycol (PEG), and hydrochloric acid (HCl) at ambient temperature and pressure. Subsequently, WS₃ was reacted with hydrogen (H₂) at high temperature (1173-1373 K) in a quartz tube. The produced WS₂ nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), and transmission electron microscopy (TEM). The characterization results indicated that the high-purity (100%) IF-WS₂ nanoparticles were produced. Moreover, addition of surfactant (PEG) and higher operating temperature (1173-1373 K) decreased the particles agglomeration, and consequently led to the reduction of average diameter of WS₂ particles in the range of 50-78 nm. The developed method is simple, environmentally compatible, and cost-effective in contrast to the conventional techniques.     

Synthesis of single-crystalline Ce(CO3)(OH) with novel dendrite morphology and their thermal conversion to CeO2

Single-crystalline cerium carbonate hydroxide (Ce(CO₃)(OH)) with dendrite morphologies have been successfully synthesized by hydrothermal method at 150 °C using Ce(NO₃)₃·6H₂O as the cerium source, aqueous carbamide as both an alkaline and carbon source and poly(vinyl pyrrolidone) (PVP) as surfactant. Ceria (CeO₂) with dendrite morphologies have been fabricated by a thermal decomposition-oxidation process at 500 °C for 6 h using single-crystalline Ce(CO₃)(OH) dendrites as the precursor. The dendrite morphologies of Ce(CO₃)(OH) was sustained after thermal decomposition-oxidation to CeO₂. The as-prepared products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TG).     

Formation of novel morphologies of aragonite induced by inorganic template

A glass-slice was used as a template to induce formation and assembly of aragonite. Thermodynamic theory was applied to explain the production of the aragonite. Transformation of three-dimensional nucleation to template-based two-dimensional surface nucleation caused the production of aragonite. Hemisphere, twinborn hemisphere and flower-shaped particles were produced by direction of the glass-slices. Planes were always appeared in these as-synthesized samples because the nucleation and the growth of these samples were adsorbed at the surfaces of the glass-slices. The formation mechanism of the as-formed sample was proposed. Compared with organic template, the present study provides a facile method to apply inorganic template to prepare functional materials.     

Growth of vaterite with novel morphologies directed by a collodion membrane

Calcium carbonate (CaCO₃) crystals were synthesized by a simple CO₂-diffusion method. A collodion membrane was employed to direct growth of CaCO₃ crystals. Polymorphs transformation was obtained at different temperatures, in which the vaterite transferred to the calcite, and the calcite transferred to the aragonite with increase of the experimental temperature. Dissolution-recrystallization processes can be used to explain these changes. At 28 °C, hexagonal slices of vaterite were firstly produced, for which the membrane was thought to be the main reason. In order to decrease surface energy, these slices assembled into various superstructures, in which hexagonal cake-like particles were the most stable among these superstructures. The cake-like vaterite transferred to the calcite through dissolution-recrystallization processes with increase of the aging time. The interested phenomenon is that the inside of the cake-like vaterite was dissolved firstly, in which the cake-like vaterite with inner hollow was determined. The membrane may induce this change.     

Hydrothermal synthesis and magnetic properties of Co0.2Cu0.03Fe2.77O4 nanoparticles

Co_0.2Cu_0.03Fe_2.77O₄ nanoparticles with different morphologies have been synthesized directly via a simple hydrothermal method. The effects of pH value, precursor concentration, reaction temperature and surfactant on the particle size were discussed. X-ray diffraction analyses showed that the as-synthesized Co_0.2Cu_0.03Fe_2.77O₄ nanoparticles possessed typical spinel structure. Scanning electron microscope images showed different morphologies of the particles, including truncated octahedron and octahedron. It was indicated that well-dispersed Co_0.2Cu_0.03Fe_2.77O₄ nanoparticles can be synthesized at pH values ranging from 11 to 13, and reaction temperature of 160 °C. The particle size decreased from 18 to 10 nm after the addition of sodium dodecyl sulphate at the pH value of 9. The magnetic measurement showed that the as-prepared Co-Cu spinel ferrite nanoparticles possessed hard magnetic property.     

Preparation of CaO as OLED getter material through control of crystal growth of CaCO3 by block copolymers in aqueous solution

As the starting materials of organic light-emitting diode (OLED) getter, calcium carbonate (CaCO₃) particles with various shapes and crystal structures have been successfully prepared with additives (L64 or PEGPG), which contain blocks of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO). These CaCO₃ particles were calcinated into highly crystalline calcium oxide (CaO) nanoparticles with high capacity of water adsorption up to 14.23 wt.%. The CaCO₃ and CaO particles prepared at various conditions were characterized using the field emission scanning electron microscopy (FE-SEM), Fourier transform infrared microscopy (FT-IR), X-ray powder diffraction (XRD), and dynamic vapor sorption (DVS) method.     

Transitions of calcium carbonate crystals controlled by self-assembly supermolecule of β-cyclodextrin and sodium dodecyl benzene sulfonate

The transitions from vaterite to calcite and from vaterite to aragonite, were found with the anionic surfactant sodium dodecyl benzene sulfonate and β-cyclodextrin as a template, respectively, when the experimental temperature was controlled at 90 °C. The transition from calcite to aragonite was found when the experimental temperature was controlled at 120 °C. The molar ratio of 1:1 and 1:2 supermolecules composed of sodium dodecyl benzene sulfonate ion and β-cyclodextrin molecule may be formed at 90 and 120 °C, respectively. The possible formation mechanisms of different CaCO₃ polymorphs are proposed based on the “structural correspondence”.     

Preparation and characterization of porous Nb2O5 nanoparticles

Porous niobium oxide (Nb₂O₅) nanoparticles have been successfully prepared without any surfactant assisting. They were characterized by X-ray diffraction (XRD), nitrogen sorption, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that the porous Nb₂O₅ nanoparticles are polycrystalline, the Brunauer–Emmett–Teller (BET) surface area is 12.09 m²/g and the average pore size is 3.4 nm. In addition, spherical and flake-like Nb₂O₅ samples were obtained and characterized. Possible explanations for the formation of Nb₂O₅ nanocrystals with different morphologies are discussed.     

Microhardness studies on calcium hydrogen phosphate (brushite) crystals

Vicker's and Knoop microhardness studies were carried out on grown calcium hydrogen phosphate dihydrate (CaHPO₄·2H₂O) crystals over a load range of 10-50 g. The Vickers (H_V) and Knoop (H_K) microhardness numbers for the above loads were found to be in the range of 94-170 kg/mm² and 28-35 kg/mm² respectively. It was also found that these numbers increased with increase in load. The Mayer's index (n) was found to be greater than 1.6 showing soft-material characteristics. The fracture toughness values (K_c), determined from measurements of crack length, were estimated to be 6 ± 0.5 × 10³ kg m^−3/2 and 4.5 ± 0.5 × 10³ kg m^−3/2 at 25 g and 50 g respectively. The brittleness indices (B_i) were found as 2.3 ± 0.1 × 10⁴ m^−1/2 for 25 g and 3.7 ± 0.1 × 10⁴ m^−1/2 for 50 g. Using Wooster's empirical relation, the elastic stiffness coefficient (c₁₁) has been calculated from Vicker's hardness values as 4.8 ± 0.5 × 10¹⁵ Pa for 10 g, 9.7 ± 0.5 × 10¹⁵ Pa for 25 g and 13.3 ± 0.5 × 10¹⁵ Pa for 50 g. The Young's modulus was calculated as 1.5 ± 0.1 × 10¹⁰ N m⁻² from Knoop microhardness values.     

Hydrothermal preparation of PbS crystals and shape evolution

In the current paper, we successfully prepared lead sulfide (PbS) microcrystals with various shapes in a simple aqueous system using the hydrothermal synthesis route. Experimental results indicated that the change of the molar ratio of Pb²⁺/S₂O₃²⁻ could significantly influence the morphology of the product while keeping the other experimental conditions constant: with the decrease of the molar ratio of Pb²⁺/S₂O₃²⁻ from 1:1 to 1:4, the shape of the products varied from tri-prism, cube to magic-square structure. Changing the reaction temperature had big effect on the shape of the product: flower-shaped product was obtained at 80 °C and cube-shaped products were produced at 120 °C. When the reaction time varied, the shapes of the as-obtained PbS crystals also changed. At the same time, SEM observations showed that the counter-anions for Pb²⁺ could influence the shape of the product: Pb(NO₃)₂ being used as lead ion sources, most flower-shaped and few cubic PbS crystals were produced; while PbSO₄ as lead ion source, the PbS cubes were obtained. An evolution process was described based on experimental facts.     

Hydrothermal preparation, characterization and property research of flowerlike ZnO nanocrystals built up by nanoflakes

In the present paper, flowerlike ZnO nanocrystals were successfully synthesized via a simple hydrothermal route in the presence of sodium dodecyl sulfate (SDS), employing Zn(CH₃COO)₂ and KOH as the starting reactants. The phase and morphology of the product were characterized by means of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and select area electron diffraction (SAED). The optical properties of the product were studied. Some factors influencing the morphology of the final product including reaction time, temperature and amounts of the surfactant were discussed. Researches showed that the flowerlike ZnO nanocrystals had a good photo-catalytic activity for degradation of safranine T under 254 nm UV light irradiation. The electrochemical research of the product showed that flowerlike ZnO nanocrystals could promote electron transfers between catechol and the Au electrode. A possible formation mechanism was also suggested based on the results of the experiments.     

Polymorph selection and nanocrystallite rearrangement of calcium carbonate in carboxymethyl chitosan aqueous solution: Thermodynamic and kinetic analysis

In this article, the polymorph selection of calcium carbonate has been successfully achieved in water-soluble carboxymethyl chitosan aqueous solution at different temperatures (25-95 °C). Vaterite is formed in carboxymethyl chitosan solution 25 °C accompanied with trace of calcite, whereas pure aragonite is obtained at 95 °C. Scanning electron microscopy and transmission electron microscopy analyses show that the products are formed from the recrystallization of nanometer crystallites. Thermodynamic and kinetic analyses reveal that the polymorph of calcium carbonate is controlled and selected by kinetics in various temperatures. As a heterogeneous nucleator and stabilizing agent, carboxymethyl chitosan changes the nucleation and growth of calcium carbonate from thermodynamic into kinetic control. Under kinetic limitation, the reaction rate of aragonite increases along with the elevating of temperature and surpasses the rate of vaterite above 327 K.