Formation Of Hollow Spheres Research Articles

Ultrasonic Spray Pyrolysis Fabrication of Solid and Hollow PbWO4 Spheres with Structure-Directed Photocatalytic Activity

Solid and hollow PbWO4 spheres were fabricated by a one-step and template-free ultrasonic spray pyrolysis (USP) using lead nitrate and ammonium metatungstate hydrate as precursors. The characteristics of the resulting samples were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption, and UV−vis diffuse reflectance spectroscopy in detail. The addition of citric acid (CA) to the precursor solution played a crucial role in producing hollow structured spheres. The hollow PbWO4 spheres were composed of single-crystal nanoparticles. On the basis of the characterization and experimental observations, a possible mechanism on the formation of solid and hollow PbWO4 spheres was proposed. Gaseous products generated due to the decomposition of CA in the pyrolysis process shaped the final hollow morphology. The results also indicated that the CA addition could decrease the crystal size of hollow PbWO4. The specific surface areas and pore volume of ...

Facile synthesis of hollow and porous nickel microspheres by low temperature molecular self-assembly

Hollow and porous nickel microspheres with potential applications as catalysts, magnetic materials, and adsorbing materials were synthesized by self-assembly in an aqueous medium in which hydrazine hydrate acted as the reducing agent. The crystal structure, phase, particle size and magnetic performance of the hollow nickel microspheres were characterized and the effects of the template, pH value, temperature, and reaction time were evaluated. Uniform hollow nickel spheres with porous structures could be obtained at 75 °C and pH of 9–10 with a heating time of 30 min. The average diameter of the spheres was 1.4 μm and mean thickness of the sphere wall was 120 nm. Polyvinyl pyrrolidone (PK40) played an important role in the formation of the spherical template which controlled the formation of hollow spheres. Magnetic measurements indicated that the hollow nickel spheres are soft-magnetic materials with much lower coercivity and much higher saturation magnetization compared to the nickel crystals with irregular shapes.

Formation of core–shell and hollow nanospheres through the nanoscale melt-solidificationeffect in the Sm–Fe(Ta)–N system

Sm–Fe–Ta–N–O nanospheres were synthesized by pulsed-laser deposition from aSm13.8Fe82.2Ta4.0 target in a nitrogen atmosphere. Three structurally and compositionallydistinct types were identified: amorphous, core–shell and hollow nanospheres.Amorphous spheres were compositionally homogeneous and completely oxidized.The core–shell spheres were composed of an iron-rich crystalline core with upto 10 at.% interstitially incorporated nitrogen, surrounded by an amorphousand oxidized shell. The hollow spheres were characterized by voids filled withN2 gas.It was found that the formation of either amorphous or complex nanospheres is defined by an initialFe/Sm ratio within the molten droplet. The formation of hollow spheres is believed to be relatedto the general affinity of liquid metals for gas intake. During rapid solidification thedissolved gas in the melt is trapped within the surrounding solid rim, preventing theoutwards diffusion of gas. As long as the amount of gas atoms in the melt is keptbelow its solubility limits it can be completely interstitially incorporated into thesolid, thus forming crystalline Fe(N)-rich cores. If the melt contains more than anequilibrium amount of nitrogen it is possible that the gas recombines to formN2 molecules, which are condensed inside the spheres.

Facile Fabrication and Optical Property of Hollow SnO2Spheres and Their Application in Water Treatment

Hollow SnO(2) spheres with smooth surface have been fabricated by a low temperature template-free solution phase route via self-assembly of small nanocrystalline particles. These hollow spheres have a very thin shell thickness of about 10 nm and are built from SnO(2) nanocrystals of an average size of 5.3 nm. The evacuation behavior of inside-out Ostwald ripening can be used to explain the formation of hollow spheres according to results of time-dependent reactions. The cathodoluminescence spectrum indicates a blue shift of the band gap emission peak of SnO(2), originating from quantum confinement effect due to the nanoscale size of SnO(2) particles. The as-prepared SnO(2) hollow spheres were also found to exhibit excellent performance in wastewater treatment.

Bio-Inducing Growth of ZnO Hollow Spheres in Lotus Root

In this paper, ZnO hollow spheres are prepared via an antitoxic bio-inducing process in lotus roots. FESEM images indicate that the tannin cells coated with ZnO are spherical with diameters ranging from 1.5 microm to 3 microm. The spheres with approximately the same size aggregate on the surface of vessels in short-range. The new bio-inducing process for formation of oxides hollow spheres might exist for long time in nature. It is proved that plant antitoxic function is the key factor to induce these structures formation. And moreover, it could be predicted that this bio-inducing phenomenon is an ideal way for preparation of materials with special structures.

A Facile Reprecipitation Method for the Preparation of Polyimide Hollow Spheres with Controllable Morphologies and Permeable Shell

Abstract We present our preliminary work on the fabrication of polyimide hollow sphere by reprecipitation. Through fine-tuning the PAA concentration, many intriguing shapes, including deflated capsules, bowl-shaped and dimple-like hollow spheres can be obtained. Adding salt to the PAA solution helps the formation of PI hollow spheres with complete shells. The morphologies can be fixed through imidization, thus obtaining a controllable and reproducible method to prepare high-performance polyimide hollow spheres with various morphologies.

Aggregates of cholic acid and benzylamine as templates for the formation of hollow silica spheres

Aggregates of cholic acid and benzylamine as templates for the formation of hollow silica spheres

Sonochemical Preparation of Hierarchical ZnO Hollow Spheres for Efficient Dye‐Sensitized Solar Cells

Hierarchical ZnO hollow spheres (400-500 nm in diameter) consisting of ZnO nanoparticles with a diameter of approximately 15 nm have been successfully prepared by a facile and rapid sonochemical process. The formation of hierarchical ZnO hollow spheres is attributed to the oriented attachment and subsequent Ostwald ripening process according to time-dependent experiments. The as-prepared ZnO hollow spheres are used as a photoanode in dye-sensitized solar cells and exhibit a highly efficient power conversion efficiency of 4.33%, with a short-circuit current density of 9.56 mA cm(-2), an open-circuit voltage of 730 mV, and a fill factor of 0.62 under AM 1.5 G one sun (100 mW cm(-2)) illumination. Moreover, the photovoltaic performance (4.33%) using the hierarchical ZnO hollow spheres is 38.8% better than that of a ZnO nanoparticle photoelectrode (3.12%), which is mainly attributed to the efficient light scattering for the former.

Fabrication of polystyrene hollow spheres in W/O/W multiple emulsions

One mild multiple emulsions was used for the fabrication of hollow polystyrene (PS) spheres. Polystyrene was dissolved in a volatile organic solvent to form the O phase, then an aqueous phase containing a surfactant was transferred into above phase to form an oil-in-water (W in/O) emulsion, followed by addition of W in/O emulsion in the external W out phase, and solvent evaporation. Final product with diameter of 150 μm, surface roughness of 30 nm, and sphericity of 98.0% was obtained. The possible influences on the formation of PS hollow sphere were also discussed.

Synthesis and characterization of Mg-doped ZnO hollow spheres

Mg-doped ZnO nanoparticles were synthesized by a simple chemical method at low temperature with Mg:Zn atomic ratio from 0 to 7%. The synthesis process is based on the hydrolysis of zinc acetate dihydrate and magnesium acetate tetrahydrate were heated under refluxing at 65 °C using methanol as a solvent. X-ray diffraction analysis reveals that the Mg-doped ZnO crystallizes in a wurtzite structure with crystal size of 5–12 nm. These nanocrystals self-aggregated themselves into hollow spheres of size of 800–1100 nm. High resolution transmission electron microscopy images show that each sphere is made up of numerous nanoparticles of average diameter 5–11 nm. The XRD patterns, SEM and TEM micrographs of doping of Mg in ZnO confirmed the formation of hollow spheres indicating that the Mg2+ is successfully substituted into the ZnO host structure of the Zn2+ site. Furthermore, the UV–Vis spectra and photoluminescence (PL) spectra of the ZnO nanoparticles were also investigated. The band gap of the nanoparticles can be tuned in the range of 3.36–3.55 eV by the use of the dopants.

Preparation of CeO2 hollow spheres via a surfactant-assisted solvothermal route

In this study, CeO2 hollow spheres were synthesized via a facile surfactant-assisted solvothermal route. The synthesized products were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and N2 adsorption–desorption. Different solvent species has been demonstrated as the key factor responsible for the controlled morphologies. Furthermore, both the water and the oleic acid were crucial to the formation of CeO2 hollow spheres. The possible formation mechanism of CeO2 hollow spheres has been preliminary discussed.

ZnO spheres and nanorods formation: their dependence on agitation in solution synthesis

ZnO nanostructures including nanorods, dense, and partially hollow spheres were synthesized via a solution synthesis method with temperature ranging from 65 to 95 °C. Scanning electron microscopy (SEM) revealed that the diameter of the spheres is in the range of 200–500 nm. Transmission electron microscopy (TEM) showed that some of the spheres are hollow or partially hollow. Powder X-ray Diffraction (XRD) and TEM-Selected area electron diffraction (SAED) analysis showed that the spheres consist of polycrystalline nanoparticles. It was found for the first time that the agitation during the synthesis plays a critical role on morphology of the ZnO nanostructures formed in solution. The oriented attachment of nanocrystals without agitation during the synthesis could guide the nanocrystals to form an ordered nanorod structure. However, the disordered aggregation of the nanocrystals under shear force resulted in a spherical morphology. It was also found that the composition of spheres is different from that of nanorods: the spheres consist of both ZnO and Zn(OH)2, but nanorods consist of single-crystal ZnO only. Zn(OH)2 presented in the spheres could decompose to ZnO by calcination, resulting in the formation of hollow spheres.

Synthesis of uniform periodic mesoporous organosilica hollow spheres with large-pore size and efficient encapsulation capacity for toluene and the large biomolecule bovine serum albumin

Large-pore periodic mesoporous organosilica (PMO) hollow spheres with controllable pore size and high pore volume (2.5 cm 3 g −1) were successfully synthesized at low-temperature (∼15 °C) by using the triblock copolymer Pluronic F127 as a template and 1,3,5-trimethylbenzene (TMB) as a swelling agent in the presence of inorganic salt (KCl). Transmission electron microscopy (TEM) measurements show that the PMO hollow spheres are uniform and well dispersed, and the composites have a large wall thickness. The influence of TMB, KCl, CTAB contents and media acidity on the mesostructure was systematically studied. The pore size (9.8–15.1 nm) of the hollow spheres can be gradually expanded by increasing TMB content together with a relatively high acidity. By controlling the content of CTAB, successive structural transformation from hollow sphere to wormlike mesostructure and eventually to ordered body-centered cubic (space group of Im-3m) mesostructure is observed. Our results reveal that the hydrophobicity of bis(triethoxysilyl)ethane (BTSE) and low-temperature approach contribute to the slow hydrolysis rate of silica precursors, which leads to weak interaction between individual TMB/F127 micelles and silicate oligomers. Furthermore, the salting-out effect of KCl may influence the swelling capacity of individual micelles as well as decrease the critical micelle concentration and critical micelle temperature, resulting in the formation of PMO hollow spheres from the assembly of individual TMB/F127 micelles with silicate oligomers. The composites exhibit efficient adsorption capacity (703 mg g −1) for toluene, suggesting they are a potentially useful adsorbent for removal of volatile organic compounds. The PMO hollow spheres allow biomolecules with large molecular weight to diffuse in, and show superior encapsulation capacity of bovine serum albumin (BSA) molecules (∼585 mg g −1) over other porous materials.

Synthesis of Hollow Zeolite Composite Spheres by Using β-Zeolite Crystal as Template

Abstract Core–shell microspheres with BEA and FAU zeolite structures (denoted as BEA–FAU) were prepared through a two-step hydrothermal crystallization process in which a β-zeolite was used as silicon source for the synthesis of Y zeolite as well as a template for the formation of hollow sphere. Scaning electron microscopy and intrusive mercury experiments displayed the as-synthesized sample had extra-large pores of 2–3 µm; a possible formation mechanism of BEA–FAU hollow spheres was proposed and discussed.

Surfactant-assisted sonochemical synthesis of hollow calcium silicate hydrate (CSH) microspheres for drug delivery

Hollow calcium silicate hydrate (CSH) microspheres with diameters around 1 μm were synthesized by a surfactant-assisted sonochemical route, and the products were characterized by XRD, SEM, FETEM and BET techniques. The results suggested that the ultrasound radiation, surfactant and Ca source were important factors which affected the formation of hollow microspheres. Based on the observation of products in different reaction systems, the possible mechanism for the formation of hollow CSH spheres was discussed. Furthermore, gentamicin, a typical anti-inflammatory drug, was used to investigate the drug loading and release behavior of the hollow spheres. The results indicated that CSH hollow spheres had high drug loading capacity and favorable drug release behavior, and might be used for preparation of bone grafts with drug delivery properties.

Controlled morphology of conducting polymers: Formation of nanorods and microspheres of polyindole

One-dimensional nanotubes and nanowires have attracted attention because of their unique electronic and mechanical properties, resulting in the promising applications in electrical, electronic and nanodevices or three-dimensional hollow spheres because of drug delivery, encapsulations and biosensor applications. For the first time we report the formation of nanorods and microspheres of polyindole conducting polymer based on chemical synthesis using two immiscible (interfacial) and two miscible solvents respectively (without surfactant). Interfacial polymerization of polyindole is carried out by taking oxidizing agent in mild acid (HCl) and monomer in dichloromethane phases and polymerization in two miscible solvents is carried out by taking monomer in ethanol and oxidizing agent in mild acidic solution. Scanning electron microscope and atomic force microscope images of polyindole confirmed the formation of hollow spheres and nanorods. The possible mechanism for controlled morphologies is discussed based on formation of metastable micelles (for microspheres) and unstable micelles (for nanorods) in absence of surfactant. The mechanism is also supported by in-situ AFM studies. FT-IR data supported the 2,3 position polymerization of polyindole in both the morphologies. XRD data revealed that nanorod are more crystalline than microspheres, however, quite different from the amorphous conventional polymer obtained by electrochemical polymerization technique.

Organic Nanostructures with Controllable Morphology Fabricated from Mixed (Phthalocyaninato)(porphyrinato) Europium Double-Decker Complexes

The self-assembly behavior of two sandwich-type mixed (phthalocyaninato)(porphyrinato) europium double-decker complexes, namely Eu(Pc)(TClPP) [Pc = phthalocyaninate; TClPP = meso-tetrakis(4-chlorophenyl)porphyrinate] (1) and optically active (R)- and (S)-EuH[Pc(OBNP)(2)](TClPP)] [Pc(OBNP)(2) = phthalocyaninate with two aromatic chiral binaphthayl units attached at the nonperipheral positions] (2), has been comparatively studied. In addition, a hydrophilic additive with intense adhesive ability, sodium carboxymethylcellulose (CMC), was also introduced onto the sandwich-type self-assembly systems to combine with double-decker molecules to induce additional hydrophilic/hydrophobic interaction. In the absence of the additive CMC, the double-decker molecules of 1 self-assemble into nanobelts in mixed solvent of chloroform and methanol. Introduction of two aromatic chiral binaphthayl units onto the nonperipheral positions of phthalocyanine ligand in the sandwich-type mixed double-decker complex 2 leads to the formation of tubal nanostructures. Observation of significant difference in the circular dichroism (CD) spectra of (R)- and (S)-2 in chloroform from their aggregates dispersed in methanol confirms the effective intermolecular interaction due to the interplay of pi-pi interaction between adjacent double-decker molecules with chiral discrimination among chiral side chains at supramolecular level. With addition of CMC, cooperation of intrinsic intermolecular pi-pi interaction with additionally introduced hydrophilic/hydrophobic interaction between adjacent double-decker molecules induces the formation of nanoscale hollow spheres at 45 degrees C during the self-assembly process of 1 and 2.

Fabrication of zinc sulphide hierarchical hollow spheres with photocatalytic property by a mild organic acid-assisted route

Large quantities of zinc sulphide hierarchical hollow spheres were successfully obtained by a mild organic acid-assisted route using zinc chloride anhydrous and thiourea as precursors. Malonic acid played a key role as a structure-directing agent in driving such hierarchical hollow spheres structures. Certain amounts of malonic acid are necessary in formation of zinc sulphide hierarchical hollow spheres. The photocatalytic properties of as-synthesised zinc sulphide hierarchical hollow spheres have been studied, which shows an excellent photocatalytic activity for the degradation of rhodamine B under ultra-violet.

Engineering the crystal growth behavior: “On substrate” MOD formation of ZnO hollow spheres

In this paper is described an easy, one-pot synthesis of ZnO hollow spheres with sizes ranging from 300 nm to 500 nm, by spin-coating deposition on aluminum substrate. Simplified models explaining the shape formation based on film–substrate interaction are discussed. The characteristic size and shape of the nanostructures obtained by the described method and the properties of ZnO as a low-cost biocompatible material make this methodology of synthesis interesting for a wide range of applications including optoelectronics, catalysis and (bio)sensors.

Electrocatalytic performance of Ba-doped TiO 2 hollow spheres in water electrolysis

Barium doped titania hollow sphere catalysts of various compositions were prepared and their electrocatalytic performance was evaluated in acidic media. Titania hollow sphere particles were prepared using poly (styrene–methacrylic acid) latex as template material, and BaCl 2 was used precursor material during barium doping over spheres. The morphology and structure of Ba/TiO 2 hollow spheres were characterized by BET, XRD, TGA and TEM analysis. XRD results had confirmed the presence of rutile TiO 2 and BaTiO 3 phases in the catalysts. The catalysts have shown almost similar surface area values (around 97 m 2/g) irrespective of their compositions. On the other hand, surface area values were diminished remarkably with rise in the calcination temperatures. In TEM images, hollow sphere formation with uniform layer of barium over the spheres could clearly be observed. Diameter of Ba-doped TiO 2 hollow sphere was found 0.4–0.5 μm irrespective of the variation in calcination temperatures. In cyclic voltammograms, both the hydrogen and oxygen evolution peaks were present for all the hollow sphere samples; although the peak positions had changed to some extent for few samples. Anodic polarization curves have shown 60 mA cm −2 current density for 20 wt% Ba/TiO 2 hollow sphere sample. Tafel slope is revealed as 122 mV for the same electrocatalyst. Barium doped titania hollow spheres have also shown long time electrocatalytic stability in acid solution.