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.     

Synthesis of monolithic alumina-silica hollow microspheres and their heat-shielding performance for adiabatic materials

Al₂O₃ ceramic foams-based composites were firstly synthesized to be used as the thermal insulation material which has excellent mechanical properties of the substrate material and better thermal properties of hollow microspheres. In this research, by doping TEOS, the monolithic hollow microspheres were prepared via a novel and effective synthesis route using propylene oxide as the gelation initiator to induce the gelation of aluminum chloride hexahydrate solution. The influence of TEOS on the morphology and high-temperature stability of the monolithic hollow microspheres was clarified in detail. Based on the optimized additive amount of TEOS, Al₂O₃ ceramic foams were introduced as the substrate material of alumina-silica hollow microspheres to fabricate the final Al₂O₃ ceramic foams-based composites. Benefited from this special structure, the Al₂O₃ ceramic foams-based composites displayed excellent mechanical properties and thermal properties. The samples changed less in appearance and did not show significant shrinkage after heat-treatment at 1200 °C. The density, bending strength and thermal conductivity of the Al₂O₃ ceramic foams-based composite were 0.32 g/cm³, 1.8 MPa and 0.12 W/m K, respectively.     

Preparation and Properties of Thermoplastic Expandable Microspheres With P(VDC-AN-MMA) Shell by Suspension Polymerization

Thermoplastic expandable microspheres (TEMs) having core/shell structure were prepared via suspension polymerization with vinylidene chloride (VDC), acrylonitrile (AN), and methyl methacrylate (MMA) as monomers and i-butane as blowing agent. TEMs were about 20 µm in diameter and had a hollow core containing i-butane. The influence of the monomer feed ratio and blowing agent content was researched. When the monomers composition of 58.4 wt% VDC, 28 wt% AN, 13.6 wt% MMA, and 32 wt% i-butane in oil phase, suspension polymerization could yield TEMs having good expansion properties. The maximum expansion volume was 25 times of original volume at about 111–120°C, the blowing agent content in microspheres was about 21.5 wt%. The T_m.e, T_o.e, and T_o.s. of the TEMs increased with the VDC content in the polymerizable monomers decreasing.     

Studies on Preparation and Hydrogen Storage Properties of Dual-Metal Ferrocenyl Coordination Polymer Microspheres

A series of dual-metal ferrocenyl coordination polymer microspheres (M₁M₂-CPMs, M₁M₂ = CoMn, CoCu, MnCu) were synthesized by the reaction of 1,1′-ferrocene dicarboxylic acid with mixed metal salts via solvothermal method. From SEM and TEM images, it was found that all the as-synthesized coordination polymers showed microspheres structures. The products were also characterized by X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FT-IR), powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). The M₁M₂-CPMs showed good thermostability and remained stable up to 250 °C. These M₁M₂-CPMs exhibited hydrogen uptake capacity. More interestingly, through the comparison among three microspheres we found that the M₁M₂-CPMs with hollow structures showed better hydrogen uptake.     

Aqueous core polystyrene microspheres fabricated via suspension polymerization basing on a multiple pickering emulsion

Multi‐hollow or hollow polymer particles are of great interest in many fields. Here we successfully fabricate polystyrene microspheres with aqueous cores through w/o/w Pickering emulsion stabilized by modified SiO₂ nanoparticles. The final structure and constituents of the microspheres is investigated via SEM, X‐ray photoelectron spectra, and thermo‐gravimetric analysis. The results demonstrate that the size and amount of aqueous cores in the microspheres can be tuned by the original structure of the multiple emulsions: when the volume fraction of inner water is 0.2, the inner structure of the microspheres obtained is porous and each pore is not interconnected; when the volume fraction of inner water is increased to 0.7, the resulting products are hollow microspheres and when 0.3% wt/vol of salt is added to the inner aqueous phase, the inner pores of the resulting microspheres enlarge or even coalesce. The multi‐hollow or hollow polystyrene microspheres with aqueous cores are expected to be candidates for encapsulation in biotechnology. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39761.     

Thermoresponsive hollow magnetic microspheres with hyperthermia and controlled release properties

Thermoresponsive hollow magnetic microspheres consisting of a hollow magnetic core, a carbon shell, and a smart polymer layer are presented in this article. A carbon nanomaterial was used as a steric stabilizer for Fe₃O₄ nanoparticles and a supporter for polymer. The thermoresponsive monomer, N‐isopropyl acrylamide, was grafted on the carbon‐encapsulate hollows by surface radical polymerization. The experimental results indicate that the composites had a phase‐transition temperature around 43°C and a saturation magnetization of 56.9 emu/g; this showed apparent thermosensitivity and magnetism. The performances in hyperthermia evaluated by an inductive magnetic field showed that the hybrid microspheres had a specific absorption rate of 240 W/g. The model drug, 5‐fluorouracil, was loaded in and released from the microspheres with different release rates at 35 and 50°C. This demonstrated that the as‐synthesized microspheres had a thermotriggered release ability and would be a good drug carrier in the biomedical field. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42617.     

Preparation of hollow SiC spheres by combustion synthesis

Hollow spherical β-SiC was successfully prepared in argon by combustion synthesis using Si powder and polytetrafluoroethylene (PTFE) powder. The phase composition and morphology of spherical products can be controlled by adjusting the Si/C₂F₄ molar ratio (M_Si/(C2F4)). When M_Si/(C2F4) = 3, the phase content of β-SiC is the highest (up to 85.54%), and hollow spherical products obtained; When M_Si/(C2F4) ≥ 5, the Si/SiC microspheres are solid. The synthesis mechanism of hollow β-SiC microspheres is as follows: Si particles react with PTFE releasing heat. Then unreacted Si absorbs heat to form liquid phase microspheres, which is equivalent to the core template to form β-SiC microspheres by reaction with cracked C. Meanwhile, the silicon diffuses from the core to the shell to form the cavity. This method can synthesize the hollow spherical β-SiC in a simple way without prearranged spherical template and long synthesis cycle.     

Carrier Mediated Transport of Thorium from Nitric Acid Medium using 2-Ethyl Hexyl Hydrogen 2-Ethyl Hexyl Phosphonate (PC88A)/N-Dodecane as Carrier

The present study deals with the application of supported liquid membrane (SLM) technique for the separation of thorium from nitric acid medium using 2-ethyl hexyl hydrogen 2-ethyl hexyl phosphonate (PC88A) as a carrier and aqueous ammonium carbonate as a receiving phase. The effects of feed acidity, nature of strippant, and membrane pore size and membrane thickness on the transport of thorium have been studied in detail. Transport behavior of uranium (²³³U) and fission products from a radioanalytical laboratory waste is also studied. Stability of the membrane against the leaching of the extractant and stability of the membrane support have been investigated. An attempt has been made to model the physicochemical transport of thorium in SLM and establish the mechanism of thorium transport. Transport of thorium increased from 25% to about 96% using 0.75 M PC88A in n-dodecane as carrier and 2 M ammonium carbonate as stripping phase as the feed acidity decreased from 4 M HNO₃ to 0.5 M HNO₃. Optimum conditions obtained from this study were applied to recover thorium and ²³³U from analytical waste generated in the laboratory.     

Facile fabrication of porous hollow CeO2 microspheres using polystyrene spheres as templates

Porous hollow CeO₂ microspheres were fabricated using negative-charged PS microspheres as templates by a facile method. The hollow CeO₂ microspheres were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and N₂ adsorption?Cdesorption. The results showed that the as-synthesized hollow CeO₂ microspheres are well monodisperse and uniform in size. The porous shells of hollow microspheres are relatively rough and composed of tiny nanoparticles. The external diameter, internal diameter, and shell thickness of hollow CeO₂ microspheres are about 190, 160, and 15?nm, respectively. A possible mechanism for the formation of hollow CeO₂ spheres was also discussed.     

Preparation magnetite core/coated with polystyrene shell hybrid materials via redox interfacial‐initiated emulsion polymerization

In this article, we describe a novel redox interfacial‐initiated micro‐emulsion polymerization (RIEP) to prepare hollow polystyrene microspheres with magnetite nanoparticles (MPs) core and polystyrene (PS) shell (MPs‐PS) under ambient pressure. The emulsion was constituted water‐based magnetic ferro‐fluid as dispersing phase and organic solvent and styrene (St) as continuous phase. Cumene hydroperoxide (CHPO)/iron (II) sulfates (FS) as the redox initiation system, the water‐soluble FS acted as the reducing component and the oil‐soluble CHPO as the oxidant component of the redox initiation system. Therefore, the primary radicals are produced mainly at the oil/water interface to initiate the polymerization of styrene to form polymer shell. The final products thoroughly characterized by X‐ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, field‐emission scanning electron microscopy, thermogravimetric analysis, dynamic light scattering, and X‐ray photoelectron spectroscopy, which showed the formation of hollow magnetite/polystyrene nanocomposite microspheres. Magnetic measurements were carried out at room temperature using a vibrating sample magnetometer. The saturation magnetization (M_s), remanent magnetization (M_r) and coercivity (H_c) is 30 emu/g, 15 emu/g and 370 Oe, respectively. The results revealed that the hybrid materials microspheres were super‐paramagnetic. POLYM. COMPOS., 31:1846–1852, 2010. © 2010 Society of Plastics Engineers     

Separation of Carrier Free 90Y from 90Sr by Hollow Fiber Supported Liquid Membrane Containing Bis(2-ethylhexyl) Phosphonic Acid

The present article gives a comparative account of the efficiency of carrier-free ⁹⁰Y separation from ⁹⁰Sr by solvent extraction, flat sheet-supported liquid membrane (FSSLM) and hollow fiber-supported liquid membrane (HFSLM) methods using bis(2-ethylhexyl) phosphonic acid (PC88A) as the carrier extractant. The major focus of this work has been to develop the HFSLM method for the separation of Y(III) on a relatively large scale. The feed and receiver phase conditions were optimized by carrying out batch solvent-extraction studies. The extraction of Sr(II) by PC88A was negligible in the acidity range of 0.01–3 M HNO₃, whereas the extraction of Y(III) was significantly large at lower acidity (≤0.1 M HNO₃) with a separation factor (SF = D_Y/D_Sr) of 8.5 × 10⁴. HFSLM studies suggested selective and efficient transport of Y(III) into 3 M HNO₃ from a feed solution containing a mixture of Y(III) and Sr(II) at 0.1 M HNO₃. On the other hand, transport of Sr(II) was negligible in the receiver phase. The purity of the separated ⁹⁰Y was ascertained by paper chromatography and by half-life measurement. The radiation stability of the carrier was excellent as studied up to 1000 KGy dose.     

Preparation of Glutathione Molecularly Imprinted Polymer Microspheres by Reversed Phase Suspension Polymerization

Molecularly imprinted polymer microspheres (MIPMs) for Glutathione had been prepared by the reversed phase suspension polymerization method; MIPMs were synthesized by using acrylamide and N-vinyl pyrrolidone as functional monomers. N,N’-methylenebisacrylamide and dimethyl diallyl ammonium chloride were the cross-linkers and H₂O₂ and Vc were redox initiators, Span-80 was the surfactant used and cyclohexane was the oil phase. Our work can provide a method to obtain ball MIPMs, and in this way, the destruction of acting sites because powdery MIPMs could be avoided. Moreover, the low concentration of cross-linker results in imprinted sites not being formed during the reversed phase suspension polymerization. The double cross-linkers not only solved this problem, but they also enlarged the selection range of the template, monomer and cross-linker. Simultaneously, there’s obviously a significant amount of synergy between the two cross-linkers that perhaps improve the adsorption capacity and selectivity. The conditions were investigated and optimized, and the optimum conditions were obtained as follows: the ratio of n_AM/n_NVP was 2; the optimum temperature and time were 50°C and 4.5 h; and, the dosage of GSH, DMDAAC and Vc were 0.8 g, 14 g and 0.023 g, respectively, under the optimum conditions, GSH-MIPM was prepared and showed the adsorption capacity was 75 mg · g^?1. Also, based on the samples prepared at the starting process and under optimal conditions, the adsorption kinetics and adsorption isotherm were investigated and analyzed, respectively.     

Uranium Permeation Studies from Nitric Acid Medium across Supported Liquid Membrane Impregnated with PC88A and its Mixtures with Neutral Oxodonors in n-paraffin as Carriers

The permeation of U(VI) from nitric acid medium using supported liquid membrane (SLM) technique has been studied employing varying compositions of feed (uranium concentration and acidity), carrier, and receiving phase. Microporous polytetrafluoroethylene (PTFE) membranes were used as a solid support and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) either alone or as a mixture of neutral donors like tri-n-butyl phosphate (TBP), tris(2-ethylhexyl) phosphate (TEHP), and tri-n-octyl phosphine oxide (TOPO) dissolved in n-parrafin as the carrier. Oxalic acid/Na₂CO₃ solutions were used as the receiving phase. The permeability coefficient (P) of U(VI) decreased with increased nitric acid concentration up to 3 M HNO₃ and thereafter increased up to 5 M HNO₃. Uranium permeation was also investigated from its binary mixtures with other metal ions such as Zr(IV), Th(IV), and Y(III) at 2 M HNO₃ employing 0.1 M PC88A/n-paraffin as the carrier, and 0.5 M oxalic acid as the receiver phase. The presence of neutral donors in the carrier solution enhanced the permeation of U(VI) across the SLM in the following order: TEHP ～ TBP > TOPO using 0.1 M oxalic acid as receiver phase. There was significant enhancement in uranium transport for feed acidity ≤2 M HNO₃ employing 1 M Na₂CO₃ as the receiver phase. These studies suggested that 0.1 M PC88A and 0.5 M oxalic acid as carrier and receiver phases appear suitable for selective and faster transport of uranium from the uranyl nitrate raffinate (UNR) waste solutions.     

Geometrical morphology optimisation of laser drilling in B4C ceramic: From plate to hollow microsphere

Boron carbide (B₄C) ceramic plates with 400-µm thickness and hollow microspheres were used for hole machining study with a fibre laser. The diameter, hole circularity, taper angle, and recast layer were evaluated as functions of processing parameters such as the peak power and the ablation time. Scanning electron microscope (SEM) was used to observe surface morphologies of drilled materials and the attached energy-dispersive spectrometer was used for elemental analyses of recast layers around holes. Based on the results of characterisations, holes on front side were found to have a larger diameter but a worse circularity than those on back side under different conditions. The taper angle was steady near 1.8° with the increase in laser parameter values. To obtain holes on B₄C ceramic with relatively good quality, the peak power and the ablation time should be controlled to be about 40 W and in 5–10 ms. In addition, compared with previous reports, superior holes drilled on B₄C hollow microspheres with a better circularity and smooth layer on the inner wall can be obtained.     

Layer-by-Layer Engineered Superparamagnetic Polyelectrolyte Hybrid Hollow Microspheres With High Magnetic Content as Drug Delivery System

Polyelectrolyte hybrid hollow microspheres with sandwich structure of about 450 nm have been accomplished by layer-by-layer self-assembling of two modified ferroferric oxide nanoparticles, lysine modified ferroferric oxide nanoparticles (Fe₃O₄-LYs) and citrate modified ferroferric oxide nanoparticles (Fe₃O₄-CA), as the main assembling materials via electrostatic interaction for the first time. They are superparamagnetic with saturation magnetization of 45.69 emu/g, revealing their high magnetic content of 70%. As drug delivery system, they also exhibited pH-stimuli responsive controlled release of an anticancer drug doxorubicin, following the Fickian diffusion model. Their unique structure and high magnetic content make them good candidate for targeted delivery.     

Fabrication of CuO nanoparticle interlinked microsphere cages by solution method

Here we report a very simple method to convert conventional CuO powders to nanoparticle interlinked microsphere cages by solution method. CuO is dissolved into aqueous ammonia, and the solution is diluted by alcohol and dip coating onto a glass substrate. Drying at 80 °C, the nanostructures with bunchy nanoparticles of Cu(OH)₂ can be formed. After the substrate immerges into the solution and we vaporize the solution, hollow microspheres can be formed onto the substrate. There are three phases in the as-prepared samples, monoclinic tenorite CuO, orthorhombic Cu(OH)₂, and monoclinic carbonatodiamminecopper(II) (Cu(NH₃)₂CO₃). After annealing at 150 °C, the products convert to CuO completely. At annealing temperature above 350 °C, the hollow microspheres became nanoparticle interlinked cages.     

Effect of Heat on Hollow Multiphase Ceramic Microspheres Prepared by Self‐Reactive Quenching Technology

The self‐reactive quenching technology, which combines flame thermal spraying technology, self‐propagating high‐temperature synthesis (SHS), and rapid solidification, is a new method for preparation of hollow microspheres. Based on this, the effect of heat released by different exothermic systems on preparation of hollow ceramic microspheres was studied. The results show that for low‐exothermic system Si‐Sucrose‐NH₄Cl, the self‐propagating reactions cannot occur, and the quenching products are Si microspheres with porous structure. For the moderate exothermic system Al–SiO₂‐Sucrose, the quenching products consist of some grains, which are hollow spherical or nearly spherical particles and irregular powders. Formation of Al₂O₃–Si indicates possible occurrence of SHS reactions. Meanwhile, for high‐exothermic system Al–Cr₂O₃‐Sucrose‐Si‐Epoxy Resin, the quenching products consist of internal hollow spherical grains and irregular‐shaped porous particles; the phase composition mainly contains Al₂O₃, Cr₃C₂, Cr₇C₃, Cr₃Si, and mullite, showing completeness of SHS reactions. The higher the adiabatic combustion temperature of the system is, the more heat it releases is higher, and the ceramic droplets form easilier.     

Facile fabrication of hollow polyaniline spheres and its application in supercapacitor

Polyaniline (PANI) is a promising electroactive material for pseudocapacitor due to the existence of the electronic conjugation structure. Here we demonstrate a novel approach to prepare hollow polyaniline nanospheres. In this process, uniform poly (methyl methacrylate- butyl methacrylate - methacrylic acid) (PMMA-PBMA-PMAA) latex microspheres as self-sacrificial templates were rapidly prepared through an emulsion polymerization method. Then the hollow PANI (H-PANI) nanospheres were obtained directly through an in-situ chemical oxidative polymerization of aniline in the presence of PMMA-PBMA-PMAA microspheres, which can be explained by the “dissolution” of templates and phase separation between the constituent polymers. The structure and morphology of the nanophase materials have been characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectra. The specific capacitance of H-PANI is 485.5 F g^?1 at 1 A g^?1 and there is 69% performance attenuation after 500 cycles, which show a promising electrochemical performance.     

Pseudo-Emulsion Based Hollow Fiber Strip Dispersion Technique (PEHFSD): Optimization,Modelling and Application of PEHFSD for Recovery of U(VI) from Process Effluent

Abstract

Pseudo emulsion based hollow fiber strip dispersion technique (PEHFSD) is the first of its kind ever explored in radioactive environment for the extraction of uranium from acidic process streams. Permeation of U(VI) was investigated as a function of various experimental variables such as hydrodynamic conditions (flow rates of pseudo-emulsion and feed phase), concentration of U(VI) in the feed phase, concentration of tri-n-butylphosphate (TBP), HNO₃ concentration in feed phase, O/A ratio and 0.01 M HNO₃ as stripping agent in pseudo-emulsion phase. The mass transfer coefficient was calculated from the experimental results and a model has been presented for determining mass transfer characteristics. PEHFSD has been demonstrated for separation/recovery of uranium from oxalate supernatant waste generated during plutonium precipitation by oxalic acid. PEHFSD and HFSLM (hollow fiber supported liquid membrane) performance has been compared in order to analyze the efficiency of the technique.     

Study of the preparation and mechanism of formation of hollow monodisperse polystyrene microspheres by SPG (Shirasu Porous Glass) emulsification technique

In a previous study, it was found that monodisperse polystyrene (PSt) hollow particles can be prepared under special conditions by combining a Shirasu Porous Glass (SPG) emulsification technique and subsequent suspension polymerization process. That is, a mixture of styrene (St), N,N‐dimethylamino ethyl methacrylate (DMAEMA), hexadecane (HD), and initiator N, N′‐azobis(2,4‐dimethylvaleronitrile) (ADVN) was used as the dispersed phase in an aqueous phase containing poly(vinyl pyrrolidone) (PVP), sodium lauryl sulfate (SLS), and water‐soluble inhibitor. The dispersed phase was created by pushing the oil phase through the uniform pores of an SPG membrane into the continuous phase to form uniform droplets. Then, the droplets were polymerized at 70°C. It has been puzzling that hollow microspheres were obtained only when sodium nitrite (NaNO₂) was used as a water‐soluble inhibitor, while one‐hole particles were formed when hydroquinone (HQ) or diaminophenylene (DAP) was used. In this study, the mechanism of formation of the hollow microspheres was verified by measuring the variation of diameter, molecular weight distribution, and monomer conversion, and by observing morphological changes during the polymerization, as well as by changing the type and amount of hydrophilic monomer, and initiator. It was found that the diameter of the oil droplets decreased, and a large amount of secondary new particles formed immediately after polymerization started in the case of NaNO₂. However, there was no such apparent behavior to be observed when HQ or DAP was used. It was determined that the hollow particles formed due to the rapid phase separation between PSt and HD, and as a consequence, a large amount of monomer diffused into the aqueous phase to form the secondary particles. Rapid phase separation confined the HD inside the droplets, a nonequilibrium morphology. On the other hand, one‐hole particles, representing an equilibrium morphology, formed when the phase separation occurred slowly because a lot of monomer existed inside of the droplets to allow mobility of the PSt. The addition of DMAEMA allowed the hollow particles to be formed more easily by decreasing the interfacial tension between the copolymer and aqueous phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1530–1543, 2002