Nanostructured CeO2 microspheres synthesized by a novel surfactant-free emulsion

Nanostructured CeO₂ microspheres with an average diameter of 11 μm were prepared by a novel surfactant-free emulsion for the first time. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmet-Teller (BET) measurements were used to characterize the products. The images of SEM showed that the CeO₂ microspheres consisted of petal-like nanostructures with petal thickness in a range of 60 nm to 100 nm. The BET measurements showed the specific surface area of the CeO₂ microspheres exceeded 43 m²/g. The XRD analysis indicated the nanostructured CeO₂ microspheres were of cubic lattice. A possible mechanism of an interfacial precipitation reaction with the droplets of solid-stabilized emulsion as templates was proposed.     

A highly reactive catalyst for CO oxidation: CeO2 nanotubes synthesized using carbon nanotubes as removable templates

In this work, the nanocomposites, carbon nanotubes (CNTs) coated with nanosized ceria, were prepared by a facile solvothermal method. The obtained nanocomposites have a dense overlayer which is made of nanoparticles with the diameter of ～10 nm. Ceria nanotubes with a porous and hollow structure were fabricated by the removal of CNTs, which possess high surface area and remarkable thermal stability. The products were characterized by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The parameters affecting the formation of CeO₂ nanotubes were discussed in details. The key steps involved in the formation of the CeO₂ nanotubes are solvothermal modifications of CNTs and controlled calcinations. CeO₂ nanotubes have an excellent catalytic performance for the CO oxidation. The remains of the templates in the CeO₂ nanotubes are considered to play an important part in the enhanced catalytic activity for the formation of CeO_2?xC_x.     

Facile synthesis of well-defined CeO2 hollow spheres with a tunable pore structure

Herein, SiO₂@CeO₂ composite microspheres were successfully prepared via a hydrothermal assisted layer-by-layer self-assembly method employing colloid SiO₂ as the template, which was fabricated by a typical Stöber method. Monodispersed CeO₂ hollow spheres with a narrow size distribution were achieved after etching colloid SiO₂ templates through NaOH. The resultant samples were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), Fourier translation infrared spectroscopy (FT-IR), X-ray photoelectron spectrum (XPS), and Nitrogen adsorption–desorption isothermal. Specifically, the shell thickness and the mesoporous structure of the hollow sphere can be easily controlled by changing the concentration of cerium source.     

Fabrication of highly monodisperse CeO2@poly(methyl silsesquioxane) microspheres and their application in UV‐shielding films

Highly monodisperse CeO₂@poly(methyl silsesquioxane) (PMSQ) microspheres were successfully prepared by a facile chemical precipitation technique. The structures and properties of CeO₂@PMSQ were analyzed by Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy techniques. We confirmed that the PMSQ microspheres were uniformly coated by CeO₂ nanoparticles, with about an 8 nm crystallite diameter. Then, CeO₂@PMSQ was incorporated into a poly(vinyl alcohol) (PVA) matrix to fabricate PVA/CeO₂@PMSQ composite films by the casting of homogeneous solutions. The thermal and optical properties of the composite films were investigated by thermogravimetric analysis and UV–visible spectroscopy. The results show the high UV‐shielding efficiency of the composites: for a film containing 2.5 wt % CeO₂@PMSQ microspheres, about 80% UV light at wavelengths between 200 and 360 nm was absorbed, whereas the optical transparency in the visible region still remained very high. The addition of CeO2@PMSQ microspheres improved the thermal stability of the PVA films. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45065.     

Synthesis and characterization of monodisperse hollow SnO<Subscript>2</Subscript> microspheres and their enhanced sensing properties to ethanol

The monodisperse hollow SnO₂ (H-SnO₂) microspheres were successfully synthesized by the ion exchange method using sulfonated PS microspheres as a template. The structure and morphology were characterized by X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy, which confirms the hollow structure of the products. The H-SnO₂ microspheres are composed of numerous SnO₂ nanoparticles with a shell thickness of about 13 nm. The monodisperse H-SnO₂ microspheres have a high specific surface area of 55.54 m²/g, which improves the gas sensing properties toward ethanol. Gas-sensing measurement results indicate that H-SnO₂ microspheres exhibit an excellent sensitivity (103.1) toward 200 ppm ethanol at 260 °C, which is much higher than that (65.8) of SnO₂ nanoparticles.     

Hydrothermal synthesis of 3D hollow porous Fe3O4 microspheres towards catalytic removal of organic pollutants

Three-dimensional hollow porous superparamagnetic Fe₃O₄ microspheres were synthesized via a facile hydrothermal process. A series of characterizations done with X-ray diffraction, Brunauer-Emmett-Teller method, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy indicated that the production of Fe₃O₄ microspheres possessed good monodispersity, uniform size distribution, hollow and porous structural characters, and strong superparamagnetic behavior. The obtained Fe₃O₄ microspheres have a diameter of ca. 300 nm, which is composed of many interconnected nanoparticles with a size of ca. 20 nm. The saturation magnetization is 80.6 emu·g^-1. The as-prepared products had promising applications as novel catalysts to remove organic pollutants (methylene blue) from wastewater in the presence of H₂O₂ and ultrasound irradiation.     

Effect of Co substitution and magnetic field on the morphologies and magnetic properties of CeO2 nanoparticles

Pure and Co-doped CeO₂ nanoparticles were synthesized successfully by the solvothermal method. The effect of Co substitution and external magnetic field on the morphologies and magnetic properties of nanoparticles was investigated. Results showed that synthesized Co-doped CeO₂ had the face-centered cubic structure and no other impurities existed in the samples with the increase of Co concentration from 5 to 75?wt%. The increasing Co concentration made the morphologies of Co-doped CeO₂ nanoparticles vary from the hollow sphere, solid sphere to rod-like shape. The applied external magnetic field of 5T decreased the nanoparticle size effectively including the diameter of hollow sphere with low Co concentration and rod-like particles with high Co concentration. Moreover, the wall thickness of hollow sphere particles was also decreased from 35?nm to 18?nm for pure CeO₂. The Co-doped CeO₂ nanoparticles showed the weak ferromagnetic behavior. With the increase of Co concentration, the saturation magnetization (M_s) value increased first and then decreased. The Co-doped CeO₂ with 30?wt% showed the highest value of 3.65?×?10^?2 emu/g (M_s). The M_s value of Co-doped CeO₂ prepared in 5T showed an increasing trend with the Co concentration. The highest value (M_s) reached 4.21?×?10^?2 emu/g for doped CeO₂ with 75?wt% Co.     

Preparation of magnetite and tumor dual-targeting hollow polymer microspheres with pH-sensitivity for anticancer drug-carriers

The hollow poly(N,N′-methylenebisacrylamide-co-methacrylic acid) (P(MBAAm-co-MAA)) microspheres were prepared by the selective removal of poly(methacrylic acid) (PMAA) core from the corresponding PMAA/P(MBAAm-co-MAA) core-shell microspheres, which were synthesized via a two-stage distillation precipitation polymerization. The magnetic Fe₃O₄ nanoparticles onto the surface of hollow P(MBAAm-co-MAA) microspheres via partial oxidation of ferrous salt during the chemical deposition in the presence of potassium nitrate as oxidant with the aid of hexamethylene tetramine and the magnetic hollow microspheres were further functionalized with folic acid (FA) via the chemical linkage with amino groups of 3-aminopropyl triethoxysilane (APS)-modified P(MBAAm-co-MAA)@Fe₃O₄ microspheres to afford the magnetite and tumor dual-targeting hollow microspheres. The resultant dual-targeting hollow polymer microspheres with pH-sensitivity were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared-spectrometer (FT-IR), UV-vis absorption spectroscopy, and vibrating sample magnetometer (VSM). Finally, the drug loading capacities of the magnetite and tumor dual-targeting hollow P(MBAAm-co-MAA) microspheres and their releasing dependence on pH values were investigated with doxorubicin hydrochloride (DXR) as an anticancer drug model.     

Preparation of Polycarbonate Hollow Microspheres by Microencapsulation Method

For the purpose of recycling waste polycarbonate (PC) products, PC hollow microspheres were prepared using waste PC products via a microencapsulation method. In the microencapsulation process, dichloromethane was the suitable organic solvent of the oil phase, and the optimal adding amount of gelatin was 1.7 g in 70 g water. The size of the PC hollow microspheres was analyzed by scanning electron microscopy (SEM). The hollow microspheres with mean diameter from 19 to 645 µm could be obtained by varying the preparation factors. The tap density could be controlled through the manipulation of the weight ratio of W₁ and O phase and PC concentration.     

A novel mercury-media route to synthesize ZnO hollow microspheres

Zinc oxide (ZnO) hollow microspheres were prepared by templates of surfactant spheres in mercury-media for the first time. Field emission scan electron microscope (FESEM), X-ray diffraction (XRD), infrared spectra (IR) and N₂ adsorption–desorption analysis were used to characterize morphologies and structure features of the products. The obtained ZnO hollow microspheres are amorphous, 1–3 μm in diameter and 70–140 nm in wall thickness. After heat treatment at 500 °C for 2 h, the amorphous ZnO hollow spheres transform to hexagonal wurtzite structure ZnO, and retain hollow sphere morphologies. During the growth of ZnO hollow microspheres, Zn is oxidized at mercury/air interface and the formed ZnO nanoparticles are assembled on the surface of surfactant spheres. PEG plays an important role for the synthesis of ZnO hollow microspheres.     

Preparation of CeO2/ZnO nanostructured microspheres and their catalytic properties

CeO₂/ZnO nanostructured microspheres with an average diameter of about 3.8 μm were synthesized by a solid-stabilized emulsion route. The CeO₂/ZnO nanostructured microspheres were characterized with SEM, XRD, CO₂-TPD, BET measurement and size analysis. Based on the oxidative coupling reaction of methane with carbon dioxide as an oxidant, the catalytic performance of the CeO₂/ZnO nanostructured microspheres was evaluated and compared with that of the CeO₂/ZnO nanoparticles. The results showed that the surfaces of the CeO₂/ZnO nanostructured microspheres consisted of petal-like structures with a petal thickness of about 90 nm and a petal depth of 0.4 μm to 0.9 μm. Using CeO₂/ZnO nanostructured microspheres as catalysts for the oxidative coupling of methane with carbon dioxide, the conversion of methane corresponded with that using the CeO₂/ZnO nanoparticles, while the CeO₂/ZnO nanostructured microspheres had much longer operating life.     

Layer-by-layer synthesis of hollow spherical CeO<Subscript>2</Subscript> templated by carbon spheres

CeO₂ hollow spheres were successfully prepared via a layer-by-layer (LBL) method using carbon spheres as sacrificial template and hexamethylenetetramine as precipitating agent. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectrum (XPS) were used for their characterization. The obtained products exhibit hollow spherical structure with a diameter of ca. 250 nm as well as the thin shell about ca. 20 nm composed of various oriented polycrystals, and the Brunauer–Emmett–Teller (BET) surface area was measured to be 126 m² g⁻¹. Calcination temperature is found to be crucial to the integrity of the hollow spheres and has to be below 973 K to achieve well defined hollow spheres. CO conversion was used as a catalytic test reaction revealing that the activity of the hollow spherical products was substantially higher than that of the non-hollow counterpart.     

Crystal structure,microstructure, thermal expansion and electrical conductivity of CeO2–ZrO2 solid solution

CeO₂–ZrO₂ solid solution was synthesised by mechanical activation solid-state chemical reaction method and characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal dilatometer, Hebb–Wagner method and DC van der Pauw method. The effects of CeO₂ content on the crystal structure, microstructure, thermal expansion coefficient (TEC), electronic conductivity and total conductivity were investigated. XRD analysis showed that (25 and 75?mol-%) CeO₂–ZrO₂ solid solutions corresponded to tetragonal and cubic phase, and 50?mol-% CeO₂–ZrO₂ belonged to the mixture of tetragonal and cubic phases. SEM analysis showed that doping CeO₂ was helpful to the sinterability of CeO₂–ZrO₂ samples. The TECs increased from 13.27?×?10^?6 to 14.72?×?10^?6?K^?1 with increasing CeO₂ content. The electronic and total conductivities of 75?mol-% CeO₂–ZrO₂ were largest, reaching 1.02?×?10^?4?S?cm^?1 and 1.02?×?10^?2?S?cm^?1 at 850°C, respectively.     

CuO/C microspheres as anode materials for lithium ion batteries

CuO/C microspheres are prepared by calcining CuCl₂/resorcinol-formaldehyde (RF) gel in argon atmosphere followed by a subsequent oxidation process using H₂O₂ solution. The microstructure and morphology of materials are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transition electron microscopy (TEM). Carbon microspheres have an average diameter of about 2 μm, and CuO particles with the sizes of 50–200 nm disperse in these microspheres. The electrochemical properties of CuO/C microspheres as anode materials for lithium ion batteries are investigated by galvanostatic discharge–charge and cyclic voltammetry (CV) tests. The results show that CuO/C microspheres deliver discharge and charge capacities of 470 and 440 mAh g⁻¹ after 50 cycles, and they also exhibit better rate capability than that of pure CuO. It is believed that the carbon microspheres play an important role in their electrochemical properties.     

Morphological and Rheological Characteristics of PVP–CeO2 Blends

This work focuses on the flow behavior of the blend comprising polyvinyl pyrrolidone and cerium (IV) oxide (CeO₂) particles in submicron size, under low shear rates. The polyvinyl pyrrolidone–CeO₂ blends have been prepared and characterized by scanning electron microscopy, X-ray diffraction, and viscometry. The generation of core–shell morphology was verified from the scanning electron micrographs. Scanning electron microscopy shows that the blend formed is of porous nature. The particle size of CeO₂ increases with the concentration of both CeO₂ and polymer due to aggregation. The blend containing as high as 35?wt% of CeO₂ was found to exhibit pseudo-plastic response under low shear rate. The reasons for the observed morphology and other properties along with mechanism were explained. The main factor, which governs the properties of the end product, was van der Waals attractive forces that exist among the constituents of the system prepared.     

Solvent-deficient synthesis of cerium oxide: Characterization and kinetics

The reaction mechanism and kinetics of CeO₂ synthesis using a solvent-deficient method are investigated by simultaneous thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The decomposition process of the cerium(III) nitrate hexahydrate and ammonium bicarbonate precursor mixture with four observed stages is monitored using TGA/DSC measurements in a nonisothermal regime with heating rates of 5, 10, 15 and 20?°C min^?1. The proposed mechanism indicates a complex synthesis with several parallel reactions, some of which occur at room temperature. A detailed kinetic analysis is performed using isoconversional (expanded Friedman, modified Coats-Redfern and Kissinger) and model fitting (N^th order and nucleation and growth models) methods. The first three stages are best described by the N^th order model with activation energy values of 21, 53 and 90?kJ?mol^?1. The last stage, during which ammonium nitrate decomposition occurs, is best fit by the nucleation and growth model and has an activation energy of 129?kJ?mol^?1. The proposed mechanism, supported by the kinetic analysis in our study, indicates that CeO₂ has already formed before the reaction reaches 200?°C. The average crystallite size of CeO₂ synthesized at 300?°C, which was calculated from the XRD measurements and observed in the SEM and TEM data, is between 10 and 20?nm.     

水热法制备二硫化钴空心微球

以CoCl2.6H2O和Na2S2O3.5H2O为原料,在150℃的水热条件下反应12 h制备了CoS2空心微球。利用X射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对产物进行了表征,探索了不同反应条件对合成产物的影响。结果表明,所得产物为立方晶系的CoS2单相,呈空心球状,其直径约为2μm,壁厚约为100 nm。此外,反应物的量、反应温度和反应时间均对产物的形成有较大影响。     

Synthesis of pH-sensitive hollow polymer microspheres with movable magnetic core

The pH-sensitive hollow poly(N,N′-methylenebisacrylamide-co-methacrylic acid) (P(MBAAm-co-MAA)) microspheres with movable magnetic/silica (Fe₃O₄/SiO₂) cores were prepared by the selective removal of poly(methacrylic acid) (PMAA) layer in ethanol/water from the corresponding Fe₃O₄/SiO₂/PMAA/P(MBAAm-co-MAA) tetra-layer microspheres, which were synthesized by the distillation precipitation copolymerization of N,N′-methylenebisacrylamide (MBAAm) and methacrylic acid (MAA) in the presence of Fe₃O₄/SiO₂/PMAA tri-layer microspheres as seeds in acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) as the initiator. The Fe₃O₄/SiO₂/PMAA tri-layer microspheres were afforded by the distillation precipitation polymerization of MAA with 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified Fe₃O₄/SiO₂ core-shell particles as the seeds. The functional multi-layer inorganic/polymer microspheres and the corresponding hollow polymer microspheres with movable magnetic cores were characterized with transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectra, dynamic light scattering (DLS), and vibrating sample magnetometer (VSM).     

Direct synthesis of CeO2/SiO2 mesostructured composite materials via sol–gel process

A series of CeO₂/SiO₂ mesostructured composite materials was synthesized by sol–gel process using Pluronic P123 as template, tetraethylorthosilicate as silica source and hexahydrated cerium nitrate as precursor under acid condition. The as-synthesized materials with Ce/Si molar ratio ranging from 0.03 to 0.3 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), and N₂ adsorption. Characterization revealed that all samples possess ordered hexagonal mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. The fact that cerium species are present as highly dispersed CeO₂ nanocrystals in hexagonal matrix was confirmed by XRD combined with high-resolution TEM and selected area electron diffraction (SAED) analysis. Introduction of ceria to silica matrix can cause a distortion of hexagonal ordering structure and decrease pore diameter and increase the wall thickness of mesopores. Moreover, it can be found that this sol–gel route is a feasible, effective and simple method for templating synthesis of CeO₂/SiO₂ composite materials.     

One-pot hydrothermal synthesis of MoS2 nanosheets/C hybrid microspheres

Uniform MoS₂ nanosheets/C hybrid microspheres with mean diameter of 320 nm have been successfully synthesized via a facile one-pot hydrothermal route by sodium molybdate reacting with sulfocarbamide in d-glucose solutions. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). XRD patterns showed that the MoS₂ was kept as a two-dimensional nanosheet crystal and C was retained as amorphous even after their annealing treatment at 800 °C. TEM and SEM images indicated that the MoS₂ nanosheets were uniformly dispersed in the amorphous carbon. The experiment results also revealed that the appropriate amount of d-glucose had an obvious effect on the formation of uniform MoS₂ nanosheets/C hybrid microspheres. A possible formation process of MoS₂ nanosheets/C hybrid microspheres was preliminarily presented.