Sol-emulsion-gel synthesis of ceramic particles

The basic characteristics of the sol-emulsion-gel (SEG) process are described as derived from water-in-oil type emulsions when ‘water’ is replaced by an aqueous sol and ‘oil’ indicates water-immiscible organic liquids. The main roles of a surfactant in emulsion formation are discussed. Steps in the generation of ceramic particles from the SEG process through a variety of experimental options are explained. Relevant examples are described where control of surfactant contents (below and above the working range of critical micelle concentration) in a sol-emulsion can lead to oxide particles of different sizes and shapes. Attempts are made to correlate the products of high-surfactant emulsions with micelles and mesophase structures known to form by surfactant molecules in large concentrations.     

Hydrothermal synthesis of SnO2 hollow microspheres

SnO₂ hollow microspheres have been synthesized by a hydrothermal method. X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were used to characterize such hollow microspheres. SEM image shows that SnO₂ microspheres with diameters of 0.5–1 μm are composed of SnO₂ nanoparticles with about 15 nm in diameter. Some broken microspheres indicate the hollow spherical structure. XRD shows that SnO₂ hollow microspheres have tetragonal structure.     

Template-free hydrothermal synthesis of hollow hematite microspheres

Hollow hematite (α-Fe₂O₃) microspheres with an average diameter of 3-4 μm and a shell thickness of approximate 150 nm was synthesized by a simple hydrothermal route using FeCl₃·6H₂O solution and acetic acid without using any templates. The hollow microspheres were composed of α-Fe₂O₃ nanoparticles with the diameter range from 20 to 40 nm. The effects of reaction parameters such as reaction time, temperature, concentration of FeCl₃·6H₂O solution, and initial pH on the morphology of the final products were investigated. A possible formation mechanism of hollow α-Fe₂O₃ microspheres was also proposed, where the acetic acid played a role of etching in the formation of hollow structure.     

Microwave-assisted synthesis of hydroxyapatite hollow microspheres in aqueous solution

We report a template-free microwave-assisted hydrothermal method for the preparation of hydroxyapatite hollow microspheres constructed by the self-assembly of nanosheets using Ca(CH₃COO)₂, Na₂HPO₄, NaH₂PO₄ and sodium citrate in aqueous solution. X-ray powder diffraction (XRD) patterns indicated that the as-prepared samples consisted of hydroxyapatite. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) micrographs showed that the as-prepared products were composed of hollow microspheres assembled with nanosheets and had three-dimensional nanoporous nanostructured networks. The experimental parameters were varied to investigate their effects on the product, and a possible formation mechanism was proposed. The as-prepared hydroxyapatite hollow microspheres have a potential application in drug delivery.     

Template-free synthesis of NiO hollow microspheres covered with nanoflakes

α-Ni(OH)₂ hollow microspheres precursors were synthesized without any template through a solvothermal method. Hydrolyzing NiCl₂ in alkaline solution, the Ni(OH)₂ hollow microspheres covered with a disordered covering of perpendicular nanoflakes were prepared. Subsequently, the similar microstructured NiO hollow microspheres with BET area around 222.8 m²/g and specific pore volume around 0.5 cm³/g were obtained by calcining the above precursor at 250–300 °C with a slow heating rate (about 1 K/min). The effects of the surfactant and the calcining temperature on the morphology and the mesostructure of the NiO hollow microspheres were also discussed.     

Chemical vapor deposition synthesis and photoluminescence properties of ZnS hollow microspheres

ZnS hollow microspheres were prepared via a facile template-free chemical vapor deposition (CVD) route using metallic zinc powders and sulphur sublimed as reactants. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectrometer (EDX). The results showed that the as-prepared ZnS hollow spheres had uniform size about 4–8 μm in diameter. The growth mechanism of such interesting was discussed. The optical property of the products was also recorded by means of photoluminescence (PL) spectroscopy.     

Additive-free and time-saving microwave hydrothermal synthesis of hollow microspheres structured boehmite

In this study, by using Al₂(SO₄)₃ aqueous solution and urea as raw materials, hollow microspheres structured boehmite was successfully synthesized only after 30 min reaction time at 180 °C via an additive-free and time-saving microwave hydrothermal route. The final products were characterized by techniques of X-ray diffraction (XRD), transmission electronic microscope (TEM), scanning electron microscope (SEM) and Fourier transform infrared spectrometry (FTIR). To investigate its crystal form and morphology evolution process, samples subjected to different reaction durations were prepared and characterized. The pivotal influence factors on boehmite morphology, such as reaction temperature, dosage of urea and microwave power range were discussed based on the experiment facts.     

A facile approach for the synthesis of uniform hollow β-CuSCN microspheres

Hexagonal β-CuSCN hollow microspheres with average diameter 5?µm were successfully synthesised on a large scale via a decomposed reaction of the Cu(II)-dithizonate complex (Cu(HDZ)₂). Examination of the produced microspheres as a function of the reaction time showed that the surface topography of the microspheres changed from a ragged surface to a smooth one. The synthetic products have been characterised by X-ray powder diffraction patterns, microscopy image and scanning electron microscopy. The optical properties were also investigated by the room temperature ultraviolet–visible absorption spectroscopy. Then, based on the observation, a possible formation process of hollow microspheres was proposed.     

Preparation of hollow hydroxyapatite microspheres

The preparation of hollow hydroxyapatite (HA) microspheres as potential drug-delivery vehicles was investigated. A lithium-calcium-borate (10Li₂O-15CaO-75B₂O₃) (mol%) glass, made by fusing the components at 1100°C for 1 h, was ground to a powder and passed through a flame at ∼1400°C to spheroidize the particles. The resulting glass microspheres (106–125 μm in diameter) were reacted in 0.25 M K₂HPO₄ solution for 5 days at 37°C and pH 10–12, resulting in the formation of porous, hollow microspheres of a calcium phosphate (Ca-P) material with external diameters similar to those of the original glass particles. Heat treatment at 600°C for 4 h partially converted the Ca-P material to HA, as confirmed by X-ray diffraction, and also increased the strength of the hollow microspheres.     

One-pot synthesis of porous hematite hollow microspheres and their application in water treatment

Alpha-Fe2O3 hollow micospheres have been successfully synthesized by solvothermal method at 200 degrees C. The synthesized products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and the nitrogen adsorption-desorption isotherm technique. The alpha-Fe2O3 hollow microspheres have an average diameter of 2-3 microm, the shell consists of numerous aligned nanorods with length of about 200-400 nm. The effects of solvent and reaction time have been studied. The Ostwald ripening mechanism is proposed to account for the formation of alpha-Fe2O3 hollow microspheres. Because of the porous hollow microstructure and large specific surface area, the microspheres were found to be effective sorbents for the removal of Cr(VI) ions from wastewater.     

有机聚合物空心微球的研究进展

有机聚合物空心微球具有独特的性能和广阔的应用前景,是近年来聚合物领域重要的研究热点。本文将近年来研究出现的有机聚合物空心微球分为普通型、功能型、杂化型、带可移动核型四大类,对它们的研究进展进行详细系统的综述。     

单分散中空聚苯乙烯微球制备

采用搅拌乳化方法制备水包油(W1/O)型乳状液,经膜乳化法制得单分散的复乳(W1/O/W2)型乳状液,再通过液中干燥法制得单分散中空聚苯乙烯(PS)微球.考察了shirasu porous glass(SPG)膜孔径对乳状液液滴粒径及粒径分布、表面活性剂浓度对PS微球中空率和单分散性的影响.由激光粒度分析仪结果及PS微球的SEM照片证实,制得的PS微球,粒径呈单分散,是SPG膜孔径的2.0～2.4倍且具有中空结构.     

Synthesis of hollow lead sulfide microspheres

Lead sulfide (PbS) uniform hollow spheres have been successfully synthesized by γ-irradiating PMMA–CS₂–ethanol aqueous solution that contains Pb(CH₃COO)₂·3H₂O at room temperature. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron micrograph (TEM), and high-resolution transmission electron micrograph (HRTEM) experimental results show that the diameter of PbS hollow spheres, the thickness of sphere shell, and the size of these crystallites are about 500, 20, and 10 nm, respectively. Room temperature UV–vis absorption spectrum of the PbS hollow spheres gives its peak centered at around 238 nm and a weak shoulder peak centered at about 322 nm. The obvious blue shift of the absorption peak may be attributed to the small dimension of the PbS bricks of the spheres wall. A possible growth mechanism of PbS hollow sphere is also presented. The successful preparation of PbS hollow spheres in large scale under mild conditions could be of interest for both applications and fundamental studies.     

Characterisation of hollow Russian doll microspheres

Poly(1-methylpyrrol-2-yl)squaraine (PMPS) particles have been characterised using SEM. The PMPS particles were used as templates to prepare bare silica and iron–silica hollow spheres, which were characterised using TEM and SEM. The PMPS particles and the hollow spheres are not uniformly sized and are agglomerated. The hollow spheres with larger diameters (>900 nm) contain an internal ‘Russian doll’ structure. The iron–silica hollow spheres are fused to one another, and the hollow spheres have a heterogeneous wall thickness. The silica and iron–silica hollow spheres both aggregate by size. There are two different size populations (for the diameter) of the bare silica and iron–silica hollow spheres. The smaller silica spheres have thinner walls compared to the larger silica hollow spheres. The larger silica hollow spheres and the iron–silica hollow spheres have similar wall thicknesses. The iron compound in the iron–silica hollow spheres has an oxidation state of 3+ and is crystalline.     

Ionic liquid assisted hydrothermal synthesis of hollow vesicle-like MoS2 microspheres

The preparation of MoS₂ microspheres with hollow vesicle-like structure was successfully achieved, which used hydrazine solution with (NH₄)₂MoS₄ as the precursor. The reaction process was assisted by a convenient ionic liquid (1-butyl-3-methylimidazolium chloride) with the hydrothermal method at 200 °C for 24 h. X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) techniques were used to characterize the samples. It was shown that the MoS₂ microspheres had uniform spherical morphology with the diameter of 1-2 μm. It was also indicated that the hollow vesicle monomers on the surface of microspheres were structured with multi-layer of MoS₂, whose d spacing was 1.0 nm. A tentative formation mechanism was proposed for the growth process of the MoS₂ microspheres with hollow vesicle-like structure.     

Controlled synthesis of hollow calcite microspheres modulated by polyacrylic acid and sodium dodecyl sulfonate

Hollow CaCO₃ microspheres were successfully synthesized through the precipitation reaction of Na₂CO₃ with CaCl₂ in the presence of polyacrylic acid (PAA) and sodium dodecyl sulfonate (SDS) at 80 °C. The concentration of SDS is an important factor to control the synthesis of hollow CaCO₃ microspheres. X-ray diffraction confirmed that the hollow CaCO₃ microsphere consists of calcite crystals. The “pearl-necklace model” of PAA/SDS micellar aggregates serves as the spherical templates to generate hollow microspheres of CaCO₃ crystals in the precipitation system.     

Novel PEGylated pH-sensitive polymeric hollow microspheres

Novel PEGylated pH-sensitive poly[methacrylic acid-co-poly(ethylene glycol) methyl ether methacrylate] [P(MAA-co-PEGMA)] hollow microspheres were synthesized by a two-stage distillation precipitation polymerization. PMAA@P(MAA-co-PEGMA) core shell microspheres were synthesized by the second-stage polymerization of MAA and PEGMA, using the N,N′-methylenebisacrylamide (MBAAm) as crosslinker in the presence of non-crosslinked PMAA microspheres. The cavity was formed by selective removal of PMAA core in ethanol. The resulted PEGylated hollow microspheres were characterized with Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FT-IR). The shrink and swelling behavior under different pH was studied by Dynamic Light Scattering (DLS).     

Biologically formed hollow cuprous oxide microspheres

Hollow cuprous oxide (Cu₂O) microspheres with a diameter of ca. 1.8 μm are prepared by using yeast as template. The possible mechanism for the formation of the hollow Cu₂O spheres is revealed. The biotemplated sample is investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet–visible (UV–vis) absorption spectra. The sample consists of the crystalline Cu₂O microspheres with diameters of about 59.5 nm and lattice parameter of 4.264 Å. The observed optical band gap of the product indicates that the blue–shift effect occurs, which is attributed to the hollow Cu₂O microspheres.