Hydrothermal synthesis of spindle-like ZnS hollow nanostructures

Spindle-like hollow nanostructures of zinc sulfide (ZnS) have been successfully synthesized by hydrothermal process using a simple surfactant emulsion template. The morphologies of ZnS nanostructures were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and field-emission scanning electron microscopy (FE-SEM). It is found that most of the products including twin ellipsoids with connected hollow cores are reminiscent of spindle-like structures. The lengths, widths and the thickness of the shell are in the range of 1-2 μm, 300-450 nm and 20-40 nm, respectively. Selected area electron diffraction (SAED) and X-ray powder diffraction (XRD) patterns show that the shell is composed of sphalerite ZnS polycrystals.     

Rapid synthesis of TiO2 hollow nanostructures with crystallized walls by using CuO as template and microwave heating

In this paper, TiO₂ hollow nanostructures with anatase walls have been rapidly fabricated by using CuO as template and microwave heating. These TiO₂ hollow nanostructures have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Experimental results showed that the TiO₂ shell transformed from amorphous to anatase phase in 3 min, induced by the hot CuO core under microwave irradiation. The diameter of TiO₂ hollow nanostructures is about 50-80 nm, and the length is about 200-300 nm. The thickness of the shell is about 3 nm. This method is promising to be used to synthesize other nanomaterials with a hollow nanostructure.     

Preparation and application of magnetic cobalt/SiO2 core/shell nanospheres

Homogeneous SiO₂-coated cobalt nanospheres with tunable silica shell thickness from 21.7 nm to 4.5 nm were synthesized by using modified Stöber method. These nanocomposites were used as source materials to prepare SiO₂ semi-hollow and hollow nanospheres by partially and completely etching cobalt cores, respectively. A proposed formation mechanism of these Co/SiO₂ nanospheres with a core/shell structure was presented in this paper, which is also important for the rational design and synthesis of other monodisperse core/shell nanoarchitectures with uniform size and shape. Furthermore, these Co/SiO₂ nanospheres were also used as a substrate for the deposition of CdS nanocrystals to prepare magnetic luminescent Co/SiO₂/CdS nanocomposites.     

Facile preparation of titania hollow spheres by combination of the mixed solvent method and the sol-gel process and post-calcination

Polystyrene (core)-titania (shell) composite spheres consisting were readily prepared by a sol-gel process of titanium tetrabutoxide (TBOT) in a mixed solvent of ethanol/acetonitrile (3:1, v/v). Smooth and homogeneous titania coatings formed when the mixed solvent was dehydrated by anhydrous sodium sulfate. The thickness and surface roughness of titania coating increase with increase of the TBOT concentration. By adjusting the TBOT concentration in the range of 5.8-29.0 mM, the size of titania-coated PS spheres could be varied from 990 to 1125 nm. Calcination at elevated temperature gave dense, homogeneous, robust shells of anatase titania. The sizes of titania hollow spheres are 11.3-16.9% smaller than those of the titania-coated PS spheres as a result of calcination-induced shrinkage. The composite and hollow spheres were characterized by scanning electron microscopy, transmission electron microscopy and electron diffraction measurements. These core-shell organic-inorganic spheres and hollow ceramic spheres may have wide applications in catalysts, adsorbents, lightweight fillers, capsules, etc.     

Hollow CoNi alloy submicrospheres consisting of CoNi nanoplatelets: Facile synthesis and magnetic properties

Magnetic alloy micro/nanostructures with controllable size and morphology have drawn intensive attention due to their interesting physicochemical properties and potential applications in micro/nanodevices. In this letter, CoNi hollow submicrospheres consisting of CoNi nanoplatelets with a thickness of ca. 10 nm have been successfully synthesized via a facile wet-chemical approach free of any template or surfactant. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images indicate that the diameter and shell thickness of the as-prepared hollow submicrosphere are ca. 600 nm and 200 nm, respectively. Elemental maps demonstrate that Co and Ni elements are distributed homogeneously in the CoNi hollow submicrosphere. Magnetic measurement reveals that the hollow submicrospheres display ferromagnetic behaviour with a coercivity of 109.5 Oe.     

Preparation and optical study of CdS nanocrystals embedded phosphate glass

A new phosphate glass system with CdS nanocrystals dispersed in glass matrix was investigated. The phosphate glass composition with good stability has been used for preparation of CdS doped glasses. The CdS in the range of 0.5-7.0% has been doped into this glass composition. Effect of CdS content on the optical and other properties has been investigated. The optical characterization of the glass samples showed that with increasing concentration of CdS, there was a red shift in transmission cut-off of the glasses. From the transmission cut-off of each glass sample, the band gap of the CdS nanocrystals embedded glass was calculated. The band gap of CdS particles embedded glass was observed in the range of 3.1-4.1 eV. The present system is compared with CdS nanocrystals doped in silica based glass system. In the phosphate glass system, the UV transmission cut-off's are not sharp and the optical transmittance decreases with increasing CdS content in contrast to silica glass system. The reason for such behavior has been discussed in the present investigation. TEM of the CdS doped phosphate glasses showed CdS particle size in the range of 5-7 nm for lower concentration of CdS and 10-100 nm for higher concentration of CdS. The nanocrystals are non-uniform in size but uniformly dispersed in glass matrix.     

Preparation and characterization of Chitosan/Konjac glucomannan/CdS nanocomposite film with low infrared emissivity

Novel organic-inorganic nanocomposite films were prepared with Chitosan (CS), Konjac glucomannan (KGM) and CdS by one-step synthesis. As-prepared films were characterized by IR spectra, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and infrared emissometer (IR). The results indicated that grown CdS dendrites were formed with reaction time of 12 h for Cd²⁺ and CS/KGM, and were well dispersed in CS/KGM with an average diameter of 40 nm. The CS/KGM/CdS nanocomposite films had significantly low infrared emissivity. When the mole ratio of CdS to summation of CS&KGM construction units was 1.0 with CdS size of 10-20 nm, the film got the lowest infrared emissivity value of 0.011, which could be attributed to the strong synergism effect existing between CS/KGM and CdS dendrites.     

Synthesis and characterization of SiO2-CaO-P2O5 hollow nanospheres for biomedical applications

A ternary system of SiO₂-CaO-P₂O₅ hollow nanospheres has been successfully prepared by sol-gel method using polystyrene (PS) nanospheres as template. The inorganic shell was produced using tetraorthosilicate (TEOS) as the silica source and tri-calciumphospate as calcium and phosphorus sources, respectively. The positive surface charge of the template and the [template]/[TEOS] ratio were the key parameters for the creation of a stable primary inorganic network and the further growth of the shell. The removal of the polymeric core through a thermal treatment procedure created an inner void space with mean diameter 250 nm while the outer mean diameter was 330 nm.     

Synthesis, characterization and fluorescence property of CdS/P(N-iPAAm) nanocomposites

A novel nanocomposite in which CdS nanoparticles were embedded in poly(N-isopropylacrylamide) (P(N-iPAAm)) matrix have been fabricated. The particle size of CdS nanoparticles ranged from 10 nm to 40 nm could be adjusted with the varying of the inorganic contents. The nanocomposites have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), thermo-gravimetric analysis (TGA), high resolution transmission electron microscope (HRTEM), UV-vis absorption and fluorescence spectra (FLS) measurements. The cell volume of CdS nanoparticles embedded in polymer matrix was smaller than the standard value and the nanocomposites with 12.0% inorganic content showed a good fluorescence property.     

Highly luminescent blue emitting CdS/ZnS core/shell quantum dots via a single-molecular precursor for shell growth

Highly luminescent blue-emitting CdS/ZnS core/shell quantum dots (QDs) were synthesized in N-oleoylmorpholine by two facile steps: first, the CdS core QDs were prepared via a simple one-pot method involving a direct reaction of Cd precursor cadmium stearate and S precursor S powder in solvent N-oleoylmorpholine; second, ZnS shells were successively overcoated on CdS core through the decomposition of single molecular precursor zinc diethyldithiocarbamate. The thickness of shell was precisely tuned by controlling drip feed speed and amount of shell precursor. The obtained CdS/ZnS core/shell QDs showed the maximum photoluminescent quantum yield of 54.8% and narrow spectra bandwidth, exhibiting high monodispersity, good color purity and long fluorescent lifetimes. The CdS/ZnS core/shell QDs with tunable emission wavelength of 424–470 nm were obtained by controlling the thickness of ZnS shell overgrown on different-sized CdS QDs, which are promising materials for blue light-emitting devices.     

Bio-template route for facile fabrication of Cd(OH)2@yeast hybrid microspheres and their subsequent conversion to mesoporous CdO hollow microspheres

Cadmium oxide (CdO) microspheres with a porous hollow microstructure were prepared by a facile yeast mediated bio-template route. The yeast provides a solid scaffold for the deposition of cadmium hydroxide (Cd(OH)₂) from cadmium acetate and sodium hydroxide solutions to form the hybrid Cd(OH)₂@yeast precursor. Thermal conversions of this at above 500 °C in air have produced hollow CdO microspheres. The products were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), thermal gravimetric and differential thermal analysis (TGA-DTA), and Brunauer-Emmett-Teller (BET) surface analysis respectively. The obtained CdO microspheres have uniform size (length = 2.6 ± 0.4 μm; width = 2.0 ± 0.2 μm) and a well defined, continuous, mesoporous hollow microstructure. The shell is about 250-280 nm in thickness. The mechanism of formation of Cd(OH)₂@yeast precursor and its conversion to CdO hollow microspheres is discussed. In comparison with traditional template-directed method, the present strategy represents a general, economical and environmentally benign route for the formation of metal oxide hollow microspheres. These materials have potential applications in different fields such as encapsulation, drug delivery, efficient catalysis, battery materials and photonic crystals. The method presented can be extended to the synthesis of other inorganic hollow microstructures of different sizes and shapes by pre-selecting suitable bio-templates.     

Optical switches based on CdS single nanowire

CdS nanowires have been synthesized by a composite-hydroxide-mediated approach. The characterization of the nanowire with X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated a single-crystalline hexagonal structure growing along direction with length up to 100 μm. The UV-visible reflection spectrum demonstrated a band gap of 2.36 eV. A strong light emission centered at 543 nm was observed under different excitation wavelengths of 300, 320, 360 and 400 nm, which was further confirmed by a bright fluorescent imaging of a single CdS nanowire. The photocurrent response based on a single CdS nanowire showed distinct optical switch under the intermittent illumination of white light. The rise and decay time were less than 1.0 and 0.2 s, respectively, indicating high crystallization with fewer trap centers in the CdS nanowires. It is possible that the undesirable trapping effects on grain-boundaries for photoconductors could be avoided thanks to the single-crystalline nature of the CdS nanowires.     

A facile synthesis of novel nanorod-assembling hollow nanowires of cadmium sulfide/DBTU nanocomposite

Novel nanorod-assembling hollow nanowires of cadmium sulfide/DBTU (N,N′-dibutylthiourea) nanocomposite were synthesized by reacting CdCl₂ with in situ produced H₂S from reaction of butylamine and carbon disulfide at molar ratio 3:3 of CS₂:BuNH₂ at 50 °C. This product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SEAD), energy dispersive X-ray spectroscopy (EDAX), thermogravimetric (TG), Fourier transform infrared (FTIR) and UV-vis absorption spectra. A plausible mechanism that the extending DBTU molecules in solvent of CS₂ induce the formation of CdS/DBTU nanorods by coordinating with the formed CdS particles, and construct these nanorods to hollow nanowires via molecular interactions is proposed and discussed on the basis of experimental results. Photoluminescence (PL) of CdS/DBTU nanocomposite exhibits increasing emission intensity largely.     

Interphase synthesis of Fe3O4/CdS core-shell nanoparticles

CdS and Fe₃O₄/CdS core-shell nanoparticles were synthesized by a simple interphase method. The obtained nanoparticles were characterized by TEM, XRD and spectroscopy techniques (fluorescence and UV-vis absorption). The effects of reagent concentration on the properties of obtained nanoparticles were investigated. It was shown that the UV-vis spectra of the Fe₃O₄/CdS colloidal toluene solutions have the sharp edge at 311 nm and the long tail. The broad emission bands in the photoluminescence spectra of the Fe₃O₄/CdS organosols observed at 506, 560 and 568 nm with the increasing of cadmium oleate concentration. The thickness of CdS shell was ranged from 0.2 to 1.0 nm while the average size of the magnetite core is about 9.9 nm.     

Solid-CdS and hollow-ZnS porous submicrospheres: Direct preparation by C-S decomposition of thiol via solvothermal processing

Porous solid-CdS or hollow-ZnS submicrospheres (SMSs) were prepared by reaction of 2-mercaptoethanol as S-source with Cd²⁺ or Zn²⁺ in ethanol using solvothermal route. Without any alkaline, solid-CdS SMSs with an average diameter of 440 nm were obtained and their size distribution in the range of 390-490 nm is above 80%; With the addition of alkaline, single crystal CdS nanorods with high-temperature-stable hexagonal phase were synthesized. With or without poly(N-vinyl-2-pyrrolidone) (PVP), solid-CdS SMSs can be prepared, but the addition of the PVP leads to the preparation of relative uniform CdS-SMSs. Hollow-ZnS SMSs with an average diameter of 340 nm were obtained under the existence of alkaline. The longer reaction time hardly influences on the size of the hollow-ZnS SMSs. More or less amount of alkaline directly influences the morphology of final product. Close-ring-shaped ZnS was prepared under the existence of less alkaline. With or without PVP under preparation reaction, hollow-ZnS SMSs can also be synthesized. Thus, during preparation of either CdS or ZnS, the PVP function is not as template, but as surfactant. The BET measurement results show that the special surface areas of solid-CdS and hollow-ZnS SMSs are 25.56 and 83.55 m²/g, respectively. The adsorption of methylene blue shows that the hollow-ZnS SMSs have very strong adsorption and decomposition ability.     

Growth of quantum-confined CdS nanoparticles inside Ti-MCM-41 as a visible light photocatalyst

CdS nanocrystallites have been successfully incorporated into the mesopores of Ti-MCM-41 by a two-step method involving ion-exchange and sulfidation. The X-ray diffraction patterns (XRD), UV-vis absorption spectra (UV-vis), photoluminescence spectra (PL), Raman spectra and N₂ adsorption-desorption isotherms were used to characterize the structure of the composite materials. It is found that most of the CdS nanocrystallites are about 2.6 nm, less than the pore diameter of Ti-MCM-41. The CdS nanocrystallites inside the mesopores of Ti-MCM-41 host show a significant blue shift in the UV-vis absorption spectrum. Under irradiation of visible light (λ > 430 nm), the composite material has greater and more stable photocatalytic activity for hydrogen evolution than bulk CdS, which can be explained by the effective charge separation between the CdS nanocrystallites and mesoporous Ti-MCM-41.     

Templated synthesis of nanosized mesoporous carbons

Mesoporous carbon materials formed by nanosized particles have been synthesized by means of a nanocasting technique based on the use of mesostructured silica materials as templates. We found that the modification of the chemical characteristics of the surfactant employed allows mesostructured silica materials with particle sizes <100 nm to be synthesised. The mesoporous carbons obtained from these silica materials retain the structural properties of the silica used as template and consequently they have a particle size in the 20-100 nm range. These carbons exhibit large BET surfaces areas (up to 1300 m² g⁻¹) and high pore volumes (up to 2.5 cm³ g⁻¹), a framework confined porosity made up of uniform mesopores (3.6 nm) and an additional textural porosity arising from the interparticle voids between the sub-micrometric particles. The main advantage of nanometer-sized mesoporous carbons in relation to the micrometer-sized carbons is that they have enhanced mass transfer rates, which is important for processes such as adsorption or catalysis.     

Synthesis of size tuneable cadmium sulphide nanoparticles from a single source precursor using ammonia as the solvent

Size tuneable cadmium sulphide nanoparticles of a few nanometres in size were prepared by thermolysis of a single source precursor of cadmium xanthates with variable carbon chain length (Cd(ROCS₂)₂, where R denotes -C₂H₅, -C₄H₉, -C₈H₁₇ and -C₁₂H₂₅, respectively) in an ammonia solution. The particle size, morphology and crystallinity of these nanoparticles were characterized using X-ray powder diffractometry, transmission electron microscopy, and nitrogen adsorption/desorption techniques. The results show that hexagonal CdS nanoparticles can be produced by thermolysis of cadmium alkyl xanthate in an ammonia solution at a temperature as low as 100 °C. The size of CdS particles (between 5.60 nm and 3.71 nm) decreases with increasing length of carbon chain in the precursor, as further confirmed by UV-visible and fluorescence spectrophotometric measurements. The size tuning mechanism of CdS from cadmium alkyl xanthate is also discussed.     

Novel MoO3 and WO3 hollow nanospheres assembled with polymeric micelles

Novel β-MoO₃ and WO₃ hollow nanospheres were synthesized using a soft template of polymeric micelle with core-shell-corona architecture. Poly(styrene-b-[3-(methacryloylamino)propyl] trimethylammonium chloride-b-ethylene oxide) micelles (PS-PMAPTAC-PEO) with cationic shell block effectively produce core/shell composite particles through electrostatic interaction with anionic precursors WO₄²⁻ and MoO₄²⁻. Transmission electron microscope (TEM) images of β-MoO₃ and WO₃ have confirmed the hollow structure with average outer diameter of 42 ± 2 and 46 ± 2 nm, respectively; the hollow cavity diameters were found to be 16  ± 1 nm and 14 ± 1 nm for β-MoO₃ and WO₃, respectively. The combination of nitrogen adsorption/desorption analyses and TEM observation confirmed the presence of disordered mesopores in the shell domain of β-MoO₃ and WO₃ hollow particles.     

Preparation of h-BN nano-tubes, -bamboos, and -fibers from borazine oligomer with alumina porous template

h-BN nano-tubes, -bamboos, and -fibers were prepared separately from borazine oligomers using an alumina porous template at different wetting times of 20 h, 40 h and 2 weeks at room temperature, respectively. The borazine oligomer in the template was transformed to the h-BN nano-materials by two-step heat-treatment at 600 and 1200 °C in flowing N₂. The FT-IR result confirmed the formation of BN. TEM and SEM images showed the formation of the nano-tubes in diameters 200-300 nm with thin walls about 10-20 nm thick, nano-bamboos 200-300 nm wide with knots at the separations of 0.5-1 μm, and the nano-fibers 15-20 μm long with fine crystallized BN particles. The mechanism for the formation of h-BN nano-tubes, -bamboos and -fibers is proposed.