Hematite nanoparticles as polystyrene microsphere coatings and hollow spheres: preparation and characterization

A novel method of fabricating composite particles with core–shell structures is demonstrated. The particles comprised monodisperse submicrometer-sized copolymer latex spheres as cores and Fe₂O₃ crystallites as shells. The shell was formed by controlled hydrolysis of aqueous iron solutions, and the growth of hematite on the surface of the copolymer spheres was controlled by slow injection. Hollow spheres were obtained by calcinations of the so-coated copolymer lattices at 500°C in air. The void size of these hollow spheres was determined by the diameter of the copolymer template, and the wall thickness could be easily controlled in the range of 20–60 nm by using this coating process. The structure and the composition of the spheres were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). It can be seen that a crystallite change and a crystal phase transformation occurred during coating and calcination of the composite spheres. The formation of the composite particles is simply explained by the nucleation of iron oxide on the surface of the latex followed by growth of the iron compound shell.     

Novel one-step route for synthesizing CdS/polystyrene nanocomposite hollow spheres

CdS/polystyrene nanocomposite hollow spheres with diameters between 240 and 500 nm were synthesized under ambient conditions by a novel microemulsion method in which the polymerization of styrene and the formation of CdS nanoparticles were initiated by gamma-irradiation. The product was characterized by transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA), which show the walls of the hollow spheres are porous and composed of polystyrene containing homogeneously dispersed CdS nanoparticles. The quantum-confined effect of the CdS/polystyrene nanocomposite hollow spheres is confirmed by the ultraviolet-visible (UV-vis) and photoluminescent (PL) spectra. We propose that the walls of these nanocomposite hollow spheres originate from the simultaneous synthesis of polystyrene and CdS nanoparticles at the interface of microemulsion droplets. This novel method is expected to produce various inorganic/polymer nanocomposite hollow spheres with potential applications in the fields of materials science and biotechnology.     

Fabrication of hollow titania microspheres with tailored shell thickness

Submicron hollow spheres are an interesting class of materials that receive significant attention nowadays. Closed and mechanically robust homogeneous hollow titania microspheres with as much shell thickness as 130 nm were fabricated by coating polystyrene beads with titania nanoparticles using sol–gel chemistry and subsequently removing the core either via heating or a chemical dissolution process. The thickness of the titania shell deposited on polystyrene core was finely tuned between 100 and 130 nm by varying the concentration of titania precursor, i.e., Ti(OEt)₄ salt from 0.5 to 2 mM during the coating process. The obtained hybrid core–shell particles and hollow microspheres were characterized by scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray diffraction, and thermo-gravimetric analysis. The approach employed is well suited to the preparation of titania-coated polystyrene hybrid particles and hollow titania spheres, which can find their applications as novel building blocks with unique optical properties for fabrication of advanced materials, catalyst, and drug delivery system.     

Preparation of magnetic polystyrene latex via the miniemulsion polymerization technique

Magnetic iron oxide (magnetite, Fe₃O₄) nanoparticles were encapsulated with polystyrene to give a stable water‐based magnetic polymer latex, using the miniemulsion polymerization technique. The resulting magnetic latexes were characterized with transmission electron microscopy (TEM), dynamic light scattering (DLS), vibrating sample magnetometer measurements (VSM), and ⁵⁷Fe Mössbauer spectroscopy measurements. TEM revealed that all magnetite nanoparticles were embedded in the polymer spheres, leaving no empty polystyrene particles. The distribution of magnetite particles within the polystyrene spheres was inhomogeneous, showing an uneven polar appearance. The DLS measurements indicated a bimodal size distribution for the particles in the latexes. According to our magnetometry and Mössbauer spectroscopy data, the encapsulated magnetite particles conserve their superparamagnetic feature when they are separated in the polymer matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4802–4808, 2004     

Constructing magnetic polyaniline/metal hybrid nanostructures using polyaniline/Fe3O4 composite hollow spheres as supports

Polyaniline (PANI)/Fe₃O₄ composite hollow spheres have been successfully synthesized in one step using sulfonated polystyrene (PS) spheres as templates. The magnetic PANI hollow spheres were used as supports for noble metal nanoparticles (NPs) such as Au and Pd. The morphology, composition and magnetic properties of the resulting products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, inductively coupled plasma (ICP) atomic spectra and vibrating sample magnetometer. The catalytic activity of magnetic PANI/Au composite shells on the oxidation of dopamine was investigated by cyclic voltammetry. The obtained results provide our product with a practical application for the detection of dopamine. On the other hand, the catalytic activity of magnetic PANI/Pd composite shells on the reduction of 4-nitroaniline was investigated by spectroscopic methods and compared with Pd/C catalyst which was already widely used in industrial production.     

Preparation,Characterization of CeO2-ZrO2 Composite Hollow Microspheres and Their Application as Electrocatalysis Materials for Hemoglobin in Biosensor

Composite hollow microspheres of CeO₂-ZrO₂ were prepared by using anionic PSA latex particles as template and then calcining the PSA core particles at 600°C. The samples were characterized by XRD, TEM, TG, SEM, EDS, and FT-IR spectra. The effects of the proportion of CeO₂ on the structure of the microspheres were also studied. Electrochemical assay showed that the CeO₂-ZrO₂ composite hollow spheres hydrided with chitosan could be used as a novel biosensing material to detect the direct electron transfer of hemoglobin.     

Magnetic polystyrene nanocapsules with core-shell morphology obtained by emulsifier-free miniemulsion polymerization

Nanocapsules containing hexadecane and Fe₃O₄ magnetic nanoparticles as core materials and polystyrene as shell were produced in a new method through emulsifier-free miniemulsion polymerization using 2,2′-azobis(2-amidinopropane) dihydrochloride (V-50) as a water-soluble initiator. The effect of some parameters such as the amounts of Fe₃O₄ and initiator on morphology of resulting nanocapsules was studied. Transmission electron microscopy showed that the products had latex particles having a size range of about 300–1300 nanometer and both magnetic nanocapsules with core-shell morphology and solid particles. The phase transition temperature and phase transition heat of the produced capsules were determined by differential scanning calorimetric analyses. Thermal properties of the latex were compared with those of magneticparticles-free latex and with those of latex free of both magnetic particles and hexadecane. Thermogravimetric analysis was also used to confirm the encapsulation and to determine the amounts of hexadecane and Fe₃O₄ within the capsules.     

氮掺杂石墨烯负载的硫化镉空心球纳米复合材料的光催化性能

通过无模板法一步合成了一种新型N掺杂石墨烯负载的CdS空心球复合材料. 采用X射线衍射、透射电镜、红外光谱、紫外-可见光谱、N₂吸附-脱附、荧光光谱和X射线光电子能谱等技术对该材料进行了表征, 并在可见光照射下测试了其在降解亚甲基蓝和水杨酸中的光催化性能. 结果表明, 相对于氧化石墨烯负载硫化镉空心球和单独的硫化镉空心球, 氮掺杂石墨烯负载的硫化镉空心球具有更高的光催化活性和稳定性. 这是由于氮掺杂的石墨烯能充当优异的电子受体和传输体, 从而抑制了载流子的复合. 另外发现, 羟基自由基是可见光下降解亚甲基蓝的主要活性物种.     

Preparation of hollow silica microspheres with controlled shell thickness in supercritical fluids

This article presents a novel route to prepare hollow silica microspheres with well-defined wall thickness by using cross-linked polystyrene (PS) microspheres as templates with the assistance of supercritical carbon dioxide (SC-CO₂). In this approach, the cross-linked PS templates can be firstly prepared via emulsifier-free polymerization method by using ethylene glycol dimethacrylate or divinylbenzene as cross-linkers. Then, the silica shell from the sol–gel process of tetraethyl orthosilicate (TEOS) which was penetrated into the PS template with the assistance of SC-CO₂ was obtained. Finally, the hollow silica spheres were generated after calcinations at 600 °C for 4 h. The shell thickness of the hollow silica spheres could be finely tuned not only by adjusting the TEOS/PS ratio, which is the most frequently used method, but also by changing the pressure and aging time of the SC-CO₂ treatment. Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscope were used to characterize these hollow silica spheres.     

Ag掺杂型空心TiO2纳米微球的制备与表征及其光催化性能

通过甲基丙烯酸与苯乙烯的乳液聚合制备了表面载有阴离子的聚苯乙烯(PSt)纳米乳胶粒. 在乙醇与水的混合溶剂中, 用硅烷偶联剂乙烯基三甲氧基硅烷对其进行表面改性. 以此乳胶粒为模板, 加入钛酸四丁酯和硝酸银制备了Ag₂O掺杂型聚苯乙烯/二氧化钛(PSt/TiO₂)复合微球. 对该微球在180 °C进行液相预处理、干燥、500 °C煅烧等步骤制备了Ag 掺杂型Ag-TiO₂复合粒子. 通过扫描电镜(SEM)、透射电镜(TEM)和X射线衍射(XRD)等手段对PSt/TiO₂复合粒子及Ag-TiO₂空心粒子的形貌及晶体结构等进行了表征. 考察了Ag-TiO₂复合粒子在紫外光(365 nm)与紫外-可见光(370-760 nm)下对罗丹明B (RhB)降解的催化活性. 结果表明, 与不含银的TiO₂空心微球相比, 在紫外光照射下, 银含量(n_Ag/n_Ti)为0.1%的Ag-TiO₂复合粒子对RhB的降解率提高了11%左右; 在紫外-可见光照射下, n_Ag/n_Ti为1.0%和2.0% 的Ag-TiO₂复合粒子对RhB的降解率提高了30%左右.     

ZnO/In2O3复合空心球的制备及其光电催化葡萄糖降解性能

通过葡萄糖协助的水热以及随后的退火处理两步法成功制备了系列ZnO/In₂O₃复合空心球. X射线衍射谱(XRD)表明, 经500 ℃退火制得的ZnO/In₂O₃复合空心球中ZnO以非晶态存在, 但是随着退火温度的提高, 其逐渐转变为纤锌矿结构. 场发射扫描电子显微镜(FE-SEM)和透射显微镜(TEM)结果表明, ZnO/In₂O₃复合材料具有空心球结构, 复合纳米颗粒之间结合紧密. 将ZnO/In₂O₃复合空心球组装成薄膜光电极, 研究了其光电催化降解葡萄糖的性能. 结果表明, 700 ℃退火处理的ZnO/In₂O₃复合空心球薄膜电极可产生最高的光致电流密度. 通过光致发光光谱(PL)发现, 与ZnO或In₂O₃空心球相比, ZnO/In₂O₃复合空心球的发光强度猝灭效果明显. 这是由于复合材料中晶界处产生的p-n结电场, 降低了光生电子-空穴对的复合几率, 从而使更多的光生电子可迁移到电极表面.     

SnO2 hollow spheres:Polymer bead-templated hydrothermal synthesis and their electrochemical properties for lithium storage

SnO2 hollow spheres have been synthesized via a facile hydrothermal method using sulfonated polystyrene beads as a template followed by a calcination process in air.X-ray diffraction,scanning electron microscopy,and transmission electron microscopy show that the as-obtained SnO2 hollow spheres have a wall thickness of about 50 nm,and consist of nanosized SnO2 particles with a mean diameter of about 15 nm.Electrochemical measurements indicate that the SnO2 hollow spheres exhibit improved electrochemical performance in terms of specific capacity and rate capability in comparison with commercial SnO2 when used as anode materials for lithium-ion batteries.The enhanced performance may be attributed to the spherical and hollow structure,as well as the building blocks of SnO2 nanoparticles.     

A novel method for the fabrication of monodisperse hollow silica spheres

In this paper, we report a novel method for the fabrication of small monodisperse hollow silica spheres. In this approach, when silica shells were coated on polystyrene particles by the sol-gel method, the polystyrene cores were dissolved subsequently, even synchronously, in the same medium to form monodisperse hollow spheres. Neither additional dissolution nor a calcination process was needed to remove the polystyrene cores. Transmission electron microscopy, scanning electron microscopy, and porosity measurements were used to characterize the monodisperse hollow silica spheres.     

Degradation of methylene blue in aqueous dispersion of hollow titania photocatalyst: study of reaction enhancement by various electron scavengers

Submicrometer-sized titania hollow spheres have been synthesized by employing sulfonated polystyrene latex particles (averaged diameter: 200 nm) as a template in conjunction with the sol-gel method. Utilization of 0.20 mol/L titanium tetrabutoxide and 25 g/L latex led to the formation of anatase particles having shell thickness of about 15 nm and void diameter of about 150 nm. Photocatalytic activity of the titania hollow spheres was examined by focusing on its enhancement by electron scavengers in the photocatalytic decomposition of methylene blue (MB). The electron scavengers employed were inorganic oxidants such as ClO*3, BrO*3, IO*4, H2O2, and S2O2*8. Differences in electronegativity, atomic radius of the halogens, and the number of highly reactive radical and nonradical intermediates were proven to be important criteria for an electron scavenger to yield high efficiency in the MB photodecomposition. Based on the results, the effect of the oxidants used were found to be in the order of S2O2*8 > IO*4 > BrO*3 > H2O2 > ClO*3.     

A facile method for the preparation of monodisperse hollow silica spheres with controlled shell thickness

This article presents a facile, effective, mild synthesis process for well‐defined hollow spheres by using cationic polystyrene (PS) submicro‐particles as templates. In this approach, the cationic PS templates can be first prepared via emulsifier‐free polymerization by using the cationic monomer 2‐(methacryloyloxy) ethyltrimethylammonium chloride as comonomer, then, the silica shells from the sol‐gel process of tetraethoxysilane were coated on the surfaces of template particles via electrostatic interaction, finally the PS was dissolved in situ by modification of the reaction conditions in the same medium to form monodisperse hollow silica spheres with controlled shell thickness. Fourier transform‐infrared spectroscopy, thermogravimetric analysis, Brunauer‐Emmett‐Teller, transmission electron microscopy, and scanning electron microscope measurements were used to characterize these hollow silica spheres. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1332–1338, 2010     

Synthesis and Catalytic Activity of Cu-Incorporated MCM-41 with Spheres-within-a-Sphere Hollow Structure

Cu-incorporated ordered hexagonal mesoporous silicates （Cu-MCM-41） with spheres-within-a-sphere hollow structure have been synthesized using thermoreversible polymer hydrogel methylcellulose （MC） and cationic surfactant as co-templates, which have been characterized by scanning electron micrograph （SEM）, X-ray diffraction （XRD）, transmission electron micrograph （TEM）, and N2 adsorption-desorption isotherms. The obtained results indicate that the morphology of Cu-incorporated MCM-41 materials is ＂spheres-within-a-sphere＂ hollow structure, which is very similar to that of the alveolus. In benzene hydroxylation with H2O2, the hollow spheres show much higher catalytic activity than particles of Cu-MCM-41.     

Synthesis and characteristics of poly(N‐isopropylacrylamide‐co‐methacrylic acid)/Fe3O4/poly(N‐isopropylacrylamide‐co‐methacrylic acid) two‐shell thermosensitive magnetic composite hollow latex particles

In this study, the poly(N‐isopropylacrylamide‐methylacrylate acid)/Fe₃O₄/poly(N‐isopropylacrylamide‐methylacrylate acid) (poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA)) two‐shell magnetic composite hollow latex particles were synthesized by four steps. The poly(methyl methacrylate‐co‐methylacrylate acid) (poly(MMA‐MAA)) copolymer latex particles were synthesized first. Then, the second step was to polymerize NIPAAm, MAA, and crosslinking agent in the presence of poly(MMA‐MAA) latex particles to form the linear poly(MMA‐MAA)/crosslinking poly(NIPAAm‐MAA) core–shell latex particles. Then, the core–shell latex particles were heated in the presence of NH₄OH to dissolve the linear poly(MMA‐MAA) core to form the poly(NIPAAm‐MAA) hollow latex particles. In the third step, the Fe₃O₄ nanoparticles were generated in the presence of poly(NIPAAm‐MAA) hollow polymer latex particles and formed the poly(NIPAAm‐MAA)/Fe₃O₄ magnetic composite hollow latex particles. The fourth step was to synthesize poly(NIPAAm‐MAA) in the presence of poly(NIPAAm‐MAA)/Fe₃O₄ latex particles to form the poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA) two‐shell magnetic composite hollow latex particles. The effect of various variables such as reactant concentration, monomer ratio, and pH value on the morphology and volume‐phase transition temperature of two‐shell magnetic composite hollow latex particles was studied. Moreover, the latex particles were used as carriers to load with caffeine, and the caffeine‐loading characteristics and caffeine release rate of latex particles were also studied. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2880–2891     

反应性模板法合成硫化银中空球-银纳米粒子异质结构

以Cu₂S中空球为反应性模板, 通过在水溶液中与银离子的阳离子交换和氧化还原反应制备了大小均匀的Ag₂S中空球-Ag纳米粒子异质结构, 即Ag₂S-Ag异质中空球. 该异质结构中每个Ag₂S中空球的直径约为600 nm, 壁厚约20–30 nm, 其表面均附着一个Ag纳米粒子. 采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)和能量色散X射线谱(EDS)对所得Ag₂S-Ag异质中空球的结构和组成进行了表征. 若以CuS中空球为反应性模板, 在相似转化条件下则主要得到不含Ag粒子的Ag₂S中空球. 该结果表明, Cu₂S中的Cu(I)的还原性在Ag₂S-Ag异质中空球的形成中发挥了重要作用. 通过对所制备的Ag₂S-Ag异质中空球进行二次生长, 还可以得到Ag₂S中空球的半球表面均被Ag膜所包覆的Ag₂S-Ag异质中空球.     

Study on Fe3O4/polyaniline electromagnetic composite hollow spheres prepared against sulfonated polystyrene colloid template

Fe₃O₄/polyaniline (PANI) composite hollow spheres were prepared by using sulfonated polystyrene (SPS) microspheres as templates. The sulfonic acid groups were applied to induce absorbing Fe₃O₄ nanoparticle, and subsequently, conductive PANI was grown. Finally, the polystyrene cores were selectively dissolved to yield composite hollow microspheres with electromagnetic properties. The analysis results indicated that the adsorption of Fe₃O₄ on template core by electrostatic interaction resulted in magnetic composite microspheres. The conductivity of composite hollow spheres was remarkably increased after polyvinylpyrrolidone modification which favored the growth of PANI on SPS/Fe₃O₄ and enhanced the integrity of hollow microspheres. The saturated magnetization of the composite hollow microspheres was tuned from 2.7 to 9.1 emu/g, and the conductivity was in the range from 10^?2 to 10⁰?S/cm.     

Selective fabrication of porous iron oxides hollow spheres and nanofibers by electrospinning for photocatalytic water purification

Porous hematite (α-Fe₂O₃) hollow spheres and nanofibers could be obtained via electrospinning and subsequent thermal decomposition in air. The precursor could be fabricated by electrospinning using Fe(NO₃)₃ as the iron source and Polyvinylpyrrolidone (PVP) as a complexing reagent. Upon calcination, pure porous α-Fe₂O₃ hollow spheres and nanofibers could be obtained at 650 °C for 3 h. The novel hollow spheres have an abundantly porous structure as well as large surface areas. Benefitting from the special porous structure, narrow bandgap, and higher surface area, porous α-Fe₂O₃ hollow materials are used as visible-light-responsive photocatalysts. So we have investigated the visible light photodegradation behavior of porous hematite (α-Fe₂O₃) hollow spheres and nanofibers towards organic dyes, as Rhodamine B (RhB). The synergetic effects of higher surface area, pore structures promoted the photocatalytic efficiency for RhB degradation under visible light and contributed to achieving the enhanced and stable photocatalytic activity.