Ca-α SiAlON hollow spheres prepared by carbothermal reduction–nitridation from different SiO2 powders

The formation process of hollow spheres composed of nanosized Ca-α SiAlON particles was investigated using SiO₂ starting powders with different characteristics in particle size, shape and crystalline state. TEM observations showed Ca-α SiAlON hollow spheres composed of a large number of nanosized particles in the products prepared at 1450 °C for 120 min in nitrogen. In all systems, the Ca-α SiAlON hollow spheres were always produced through an intermediate Si–Al–Ca–O liquid phase in the same mechanism, regardless of the characteristics of SiO₂ starting powders used. Spherical solid particles consisted of amorphous phase containing Si, Al, Ca, O and a small amount of N were generated at the initial stage of carbothermal reduction–nitridation. These spherical solid particles changed into hollow particles with the progression of the reaction from the liquid phase to the crystalline Ca-α SiAlON with increasing temperature.     

Hollow microspheres of NiO as anode materials for lithium-ion batteries

NiO hollow spheres are prepared by heating the NiCl₂/resorcinol-formaldehyde (RF) gel in argon at 700 °C for 2 h, and subsequently in oxygen at 700 °C for 2 h. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to characterize the structure and morphology of the as-prepared NiO hollow spheres. These hollow spheres have a diameter of about 2 μm, which are composed of NiO particles of about 200 nm. The electrochemical properties of these NiO hollow spheres are investigated to determine the reversible capacity and cycling performance as anode materials for lithium-ion batteries, and the advantages of their hollow spherical morphology to the electrochemical performance are discussed.     

Visible-light photocatalytic activity of SiC hollow spheres prepared by a vapor–solid reaction of carbon spheres and silicon monoxide

SiC hollow spheres are obtained by a vapor–solid reaction using carbon spheres as templates. The prepared SiC hollow spheres are characterized by X-ray diffraction, scanning electron microscopy, nitrogen adsorption, and UV–vis diffuse reflectance spectra. The visible-light photocatalytic activity is evaluated by photocatalytic decomposition of the methylene blue in aqueous solution. Results show that the diameter of SiC hollow spheres ranges from 200 to 300 nm and the shell thickness is about 50 nm. The SiC hollow spheres have a high surface area of 83.5 m²/g and exhibit a mesoporous structure characteristic. The photo-response of the SiC hollow spheres expand to visible-light region with band gap energy of 2.15 eV. The SiC hollow spheres exhibit a significantly enhanced photocatalytic activity due to their high surface area as well as large light-harvesting efficiencies.     

Bi-component MnO/ZnO hollow microspheres embedded in reduced graphene oxide as electrode materials for enhanced lithium storage

Novel composite of bi-component MnO/ZnO (denoted as MZO) hollow microspheres embedded in reduced graphene oxide (RGO) as a high performance electrode material for Lithium ion batteries (LIBs) is prepared via one-pot hydrothermal method and subsequent annealing. The structures and morphologies of as-prepared hybrid materials are characterized by X-ray diffraction, scanning electron microscopy, Raman spectra, FTIR and transmission electron microscopy. The results reveal that the MZO hollow microspheres with nanometer-sized building blocks are well dispersed in the RGO support. The electrochemical tests show that the hybrid material has a reversible capacity of 660 mAh/g at a current density of 100 mA/g with a coulombic efficiency of 98% after 100 cycles. Besides, a specific capacity of about 207 mAh/g is retained even at a current density as high as 1600 mA/g, exhibiting high reversibility and good capacity retention. Our results suggest that the composite of bi-component MZO hollow microspheres embedded in RGO will be promising electrode materials for low-cost, environmentally friendly and high-performance LIBs.     

Hollow nickel microspheres covered with oriented carbon nanotubes and its magnetic property

A composite structure consisting of hollow nickel microspheres coated with oriented carbon nanotubes (CNTs) was synthesized via chemical vapor deposition at 800 °C. The hollow microspheres were composed of discrete Ni nanoparticles which acted as the catalyst. FESEM images showed that the CNTs grew on the surface of the Ni spheres. HRTEM, Raman and XRD analyses showed that the CNTs were highly graphitized. Magnetic measurements demonstrated that these composite structures exhibited enhanced ferromagnetic behaviour compared with hollow Ni spheres and bulk Ni.     

Effect of annealing process on the growth and surface properties of Au–ZnO nanowire films grown by chemical routes

Au–ZnO nanowire films have been synthesized by chemical routes, electrochemical deposition (ECD) and chemical bath deposition (CBD) techniques, on zinc foil followed by annealing in air at 400 °C. X-ray diffraction patterns reveal formation of the ZnO wurtzite structure along with binary phases Au₃Zn and AuZn₃. Scanning electron microscopy shows the presence of ZnO nanowires having several micrometers in length and less than 120 nm in diameter synthesized by ECD and in the range of 70–400 nm using the CBD technique. During the annealing process, different surface morphologies originating from different catalytic effects of Au atoms/layers were observed. In addition, the effect of synthesis routes on crystalline quality and optical properties were studied by Raman and photoluminescence spectrometers indicating varying concentration of defects on the films. The Raman results indicate that Au–ZnO nanowire film prepared by chemical bath deposition route had better crystalline quality.     

Synthesis and characterization of hollow zeolite microspheres with a mesoporous shell by O/W/O emulsion and vapor-phase transport method

Hollow microspheres of ZSM-5 with a mesoporous shell have been synthesized through formation of amorphous hollow SiO₂/Al₂O₃ microspheres by sol–gel process in multiple oil–water–oil emulsions and transformation of the amorphous species into zeolite by water–organic vapor-phase transport treatment at 160 °C for 8 days. The morphology of the amorphous and zeolite spheres observed by scanning electron microscopy shows no significant change whereas the molar ratio of Si/Al increases from 6 to 20 during the transformation. The structural feature of zeolite was characterized by X-ray diffraction and ²⁹Si and ²⁷Al magic-angle spinning nuclear magnetic resonance. Transmission electron microscopy and N₂ adsorption–desorption isotherms indicate that uniform mesopores in the shell of zeolite spheres arise from the interstices among zeolite crystallites.     

Controlled fabrication of nanosized TiO2 hollow sphere particles via acid catalytic hydrolysis/hydrothermal treatment

TiO₂ hollow spheres of controlled size were synthesized by combined acid catalytic hydrolysis and hydrothermal treatment, which involves the deposition of an inorganic coating of TiO₂ on the surface of carbon spheres prepared by a hydrothermal method and subsequent removal of the carbon spheres by calcination in air. The obtained TiO₂ hollow spheres were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and powder X-ray diffraction. The results revealed that the size and surface morphology of the TiO₂ hollow spheres can be controlled by adjusting the concentration of the aqueous solution of glucose used to produce the template carbon spheres. Increasing the concentration of the glucose solution increased the average diameter of the TiO₂ hollow spheres from 190 to 300 nm. TiO₂ hollow spheres prepared using a glucose solution with a concentration of 0.7 mol/L are uniform in size with a diameter of 220 nm and shell thickness of 28 nm. The phenol removal rate of the sample prepared by calcination at 600 °C is 1.35 times higher than that of TiO₂ made by the same method without using the carbon template.     

Synthesis and characterization of ZnSe rose-like nanoflowers and microspheres by the hydrothermal method

ZnSe rose-like nanoflowers and microspheres were successfully grown on Zn foils by the hydrothermal method at 220 °C for 36 h. Scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) spectroscopy were used to observe the morphologies, structures, chemical compositions and optical properties of the as-synthesized ZnSe samples. The XRD patterns revealed that as-synthesized ZnSe nanoflowers and microspheres have cubic zinc blende structure. The SEM observations showed that low concentration of EDTA was beneficial to obtain the ZnSe rose-like nanoflowers. With increase of EDTA concentration, the morphology of the as-synthesized samples transformed into microspheres. It was proved that EDTA played a significant role during the synthesis of ZnSe rose-like nanoflowers and microspheres. Room temperature photoluminescence (PL) spectroscopy of the samples showed that the spectra were wide band from blue light to orange light. Furthermore, a possible formation mechanism of ZnSe nanoflowers and microspheres was proposed and discussed.     

Catalytic oxidation of benzene,toluene and p-xylene over colloidal gold supported on zinc oxide catalyst

Au was loaded (1.5 wt.%) on the supports (ZnO, Al₂O₃ and MgO) by a colloidal deposition method. For a range of low temperatures (50–300 °C), the catalytic activity of Au/ZnO was much greater than that of Au/Al₂O₃ and Au/MgO. In particular, for the Au/ZnO, the benzene conversion exceeded 80% at 150 °C. The results of catalyst characterization suggested that the high catalytic activity of the Au/ZnO might be attributed to the effects of strong metal–oxide interaction which is possibly originated from the small lattice parameter difference between Au {111} and ZnO {101} lattice planes.     

Study of the anticorrosive efficiency of zincite and periclase-based core–shell pigments in organic coatings

The objective of this work was to identify the anticorrosive efficiency of synthesized, MeO/core pigments and of MeO pigments (MeO = ZnO, MgO) with varied morphology of particles. The synthesized MeO-type pigments displayed varied particle morphologies and the MeO/core core–shell pigments exhibited surface of particles made of zincite and periclase. These core–shell pigments have the properties of both the ZnO layer and of the core (wollastonite or graphite). Epoxy-ester based coatings containing the synthesized pigments were also formulated. To test the anticorrosion properties of the coatings, accelerated corrosion tests were carried out in the environment of condensed water, of NaCl mist, and of condensing water and SO₂. The synthesized core–shell pigments have good anticorrosion efficiency in an epoxy-ester coating.     

Electrodeposited nanoporous ZnO films exhibiting enhanced performance in dye-sensitized solar cells

Electrodeposition of nanoporous ZnO films and their applications to dye-sensitized solar cells (DSSCs) were investigated in the aim of developing cost-effective alternative synthetic methods and improving the ZnO-based DSSCs performance. ZnO films were grown by cathodic electrodeposition from an aqueous zinc nitrate solution containing polyvinylpyrrolidone (PVP) surfactant. PVP concentration had strong effects on the grain sizes and surface morphologies of ZnO films. Nanoporous ZnO film with grain size of 20-40 nm was obtained in the electrolyte containing 4 g/L PVP. The X-ray diffraction pattern showed that nanoporous ZnO films had a hexagonal wurtzite structure. Optical properties of such films were studied and the results indicated that the films had a band gap of 3.3 eV. DSSCs were fabricated from nanoporous ZnO films and the cell performance could be greatly improved with the increase of ZnO film thickness. The highest solar-to-electric energy conversion efficiency of 5.08% was obtained by using the electrodeposited double-layer ZnO films (8 μm thick nanoporous ZnO films on a 200 nm thick compact nanocrystalline ZnO film). The performance of such cell surpassed levels attained in previous studies on ZnO film-based DSSCs and was among the highest for DSSCs containing electrodeposited film components.     

Surfactant-free synthesis of Cu2O hollow spheres and their wavelength-dependent visible photocatalytic activities using LED lamps as cold light sources

A facile synthesis route of cuprous oxide (Cu₂O) hollow spheres under different temperatures without the aid of a surfactant was introduced. Morphology and structure varied as functions of reaction temperature and duration. A bubble template-mediated formation mechanism was proposed, which explained the reason of morphology changing with reaction temperature. The obtained Cu₂O hollow spheres were active photocatalyst for the degradation of methyl orange under visible light. A self-designed equipment of light emitting diode (LED) cold light sources with the wavelength of 450, 550, and 700 nm, respectively, was used for the first time in the photocatalysis experiment with no extra heat introduced. The most suitable wavelength for Cu₂O to photocatalytic degradation is 550 nm, because the light energy (2.25 eV) is closest to the band gap of Cu₂O (2.17 eV). These surfactant-free synthesized Cu₂O hollow spheres would be highly attractive for practical applications in water pollutant removal and environmental remediation.     

Synthesis of carbon xerogel particles and fractal-like structures

A variety of dense and open-architecture amorphous carbon xerogel microspheres and folded fractal-like structures were synthesized by sol-gel polycondensation of resorcinol with formaldehyde in a slightly alkaline aqueous solution. Carbon structures were obtained by inverse emulsification of resorcinol-formaldehyde (RF) sol in cyclohexane containing a non-ionic surfactant Span-80, followed by its pyrolysis at 1173 K in nitrogen. We have investigated the effects of synthesis parameters including stirring time, resorcinol/catalyst (R/C) ratio and surfactant concentration on the structures. The average particle size of the carbon microspheres could be modulated from 5 to 46 μm by increasing the stirring time from 2 to 7 h and by varying the R/C ratio from 0.2 to 500. Particles agglomerated as the R/C ratio increases above 100. Increase in the surfactant concentration from 1% to 4% (v/v) produced smaller spherical particles with narrower size distribution. Further increase in the surfactant concentration from 10% to 50% (v/v) produced branched and folded fractal-like structures of large external area. Thus, RF sol-based precursor chemistry can be easily tuned to produce a spectrum of desired carbon particle morphologies with potential applications in printing technology, adsorbents, resonance-based solar cells, thermal detectors and carbon-based micro-electromechanical devices (C-MEMS).     

Gas sensing performance of hydrothermally grown CeO2–ZnO composites

The sensors based on cerium oxide–zinc oxide (CeO₂–ZnO) composites were fabricated by using thick-film screen printing of hydrothermally grown powders. The structural, morphological investigations were carried out by using XRD, FESEM and TEM and these studies revealed that the synthesized products were grown in high-density and possessed well-crystallinity. Furthermore, the gas responses were evaluated towards the ethanol, acetone, liquid petroleum gas (LPG) and ammonia gases. The 2 wt% CeO₂–ZnO composite exhibited excellent response of 94% at 325 °C and better selectivity towards ethanol with low response and recovery time as compared to pure ZnO and can stand as reliable sensor element for ethanol sensor related applications.     

The characteristics of Ni–Co–Mn–O precursor and Li(Ni1/3Co1/3Mn1/3)O2 cathode powders prepared by spray pyrolysis

Ni–Co–Mn–O precursor powders with spherical shape and dense structure were prepared by spray pyrolysis from a spray solution containing a drying control chemical additive (DCCA) and polymeric precursors. In contrast, the Ni–Co–Mn–O precursor powders obtained from a spray solution without additives had a hollow and porous morphology. Ni–Co–Mn–O precursor powders with a spherical shape and dense structure yielded Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode powders with a spherical shape and fine size by means of a solid-state reaction with lithium hydroxide. The mean size of the spherical cathode powder was 1.1 μm. The discharge capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders with spherical shape and filled morphology was 195 mA h g⁻¹ at a current density of 0.1 C. The discharge capacities of the cathode powders with spherical shape and filled morphology at 55 °C decreased from 183 to 154 mA h g⁻¹ by the 30th cycle at a current density of 0.5 C.     

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.     

A CTAB-assisted hydrothermal and solvothermal synthesis of ZnO nanopowders

ZnO nanopowders were synthesized by hydrothermal and solvothermal method by using CTAB as surfactant, and the effects of CTAB on the morphologies of ZnO nanopowders were investigated. The results showed that the presence of CTAB could greatly vary the shape of the ZnO crystals. ZnO nanorods were prepared from the hydrothermal system without CTAB and flowers-like ZnO nanostructures were produced from hydrothermal system with 0.4 M and 0.5 M CTAB. Low concentration of CTAB in ethanol was conducive to the formation of ZnO nanorods, but the concentration continued to increase, the morphology of sample transformed into hexagonal bipyramid, and then transformed into spherical. The synthesis mechanism of ZnO powders with different morphologies has been presented.     

Synthesis and cathodoluminescence properties of porous wood (fir)-templated zinc oxide

Wood (fir)-templated ZnO with hierarchically porous structure has been successfully synthesized through a simple hydrothermal process. Morphology and porosity of the products were investigated by FESEM, TEM, and N₂ adsorption, respectively. The optical properties were measured by cathodoluminescence (CL) at room temperature. The morphologies of bulk and ground flake ZnO show an inheritance from the fir microstructure. Experimental results suggest that a higher calcination temperature will influence the grain size and porosity. The pore size decreases from 20 to 10 μm in the bulk ZnO, while increases from 50 nm to several micrometers in the flake ZnO when the calcination temperature changes from 600 to 1200 °C. CL spectra also show temperature-dependent properties at ultraviolet (UV) band and blue band. The intensity of visible emission originated from oxygen vacancies is proportional to the calcination temperature, while that of UV emission is inverse proportional due to quantum confinement effect.     

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.