Hydrothermal synthesis of graphene-ZnS quantum dot nanocomposites

ZnS nanodots highly dispersed on the surfaces of graphene sheets were successfully synthesized via an easy hydrothermal method by using Na₂S as reducing agent as well as sulfide source. The reduction of graphite oxide (GO) to graphene was accompanied by the deposition of ZnS particles on the surface of graphene sheets. The results of X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) demonstrate the efficient reduction of GO to graphene sheets. The morphology characterization of the sample shows a wrinkled paper-like structure of the graphene sheets decorated with ZnS nanoparticles. Moreover, photoluminescence (PL) measurement shows a smooth spectrum, indicating fewer defects in the composite.     

Fabrication of novel sol-gel silica coatings reinforced with multi-walled carbon nanotubes

Novel sol-gel silica coatings reinforced with multi-walled carbon nanotubes (MWCNTs) have been prepared using the organic sol-gel route and the dip-coating technique on magnesium alloy substrates. Homogeneous and dense composite coatings with good reinforcement dispersion were fabricated using low temperature and atmospheric pressure fabrication conditions. The presence of nanotubes caused a substantial enhancement of silica coating fracture toughness on coatings deposited on grounded substrates but it was not as effective on polished substrates because of the low adhesion of the coating to the substrate. Bridging phenomena caused by the MWCNTs was observed, indicating that an effective load transfer between the silica matrix and the nanotube reinforcement was also achieved.     

Facile synthesis of rice-like anatase TiO2 nanocrystals

Rice-like anatase TiO₂ nanocrystals have been synthesized by hydrothermal treating Ti(OH)₃ precursor in deionized water, which is easy to form in-situ a stable TiO₂ aqueous dispersion and no post-synthetic purification process is required. The influences of synthetic parameters, such as reaction time and pH value, on the morphologies of the resulting nanocrystals have been investigated. It is found that the crystallinity and sizes of TiO₂ nanocrystals increase with the reaction time increased. The pH value is important for controlling the sizes and shapes of TiO₂ nanocrystals. As pH value increases from 2 to 11, spherical, rice-like, and rod-like TiO₂ nanocrystals are obtained, respectively. The formation mechanism of rice-like anatase TiO₂ nanocrystals is supposed to be a hydrothermal crystallization and Ostwald ripening process.     

Electrical and dielectric properties of polypropylene nanocomposites based on carbon nanotubes and barium titanate nanoparticles

Functional polypropylene (PP) nanocomposites were prepared by melt compounding with multiwalled carbon nanotubes (MWNT) as the electrically conductive component and barium titanate (BT) spherical nanoparticles as the ferroelectric component. To make PP electrically conductive, more than 3 wt.% MWNT is required. Surface modification of either MWNT or BT with titanate coupling agent further improves the electrical conductivity of the PP/MWNT/BT ternary nanocomposites. Interestingly, by modifying both MWNT and BT, 2 wt.% MWNT are sufficient to make the ternary nanocomposite electrically conductive. In addition, the incorporation of MWNT greatly increases the dielectric permittivity of PP/BT nanocomposites. However, to retain a low dielectric loss, the MWNT loading should be slightly less than the percolation threshold of the nanocomposites. The improved electrical conductivity and dielectric properties make the ternary nanocomposites attractive in practical applications.     

Ionic liquid-assisted synthesis,structural characterization,and photocatalytic performance of CdS nanocrystals

With the assistance of the ionic liquid trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentylphosphinate), we have successfully synthesized short nanorods, quasi-nanospheres and faceted CdS nanoparticles via thermal decomposition of cadmium diethyldithiocarbamate complexes. It was shown that the shape, size and crystallinity of the products could be controlled through delicate regulation of the reaction temperature, monomer concentration, reaction time, and ionic liquid ratio. We found that higher temperature was beneficial to the good crystallinity, while the lower temperature and higher monomer concentration were in favor of anisotropic structures. The used ionic liquid contributed to the formation of hexagonal phase CdS nanocrystals, and its ratio played an important role in determining the ultimate morphology of products. The possible mechanism for the formation CdS nanocrystals was proposed. Furthermore, the as-prepared CdS samples demonstrated a highly photocatalytic activity in the degradation of methyl orange under visible light irradiation.     

Facile one-pot synthesis of superfine palladium nanoparticles on polydopamine-functionalized carbon nanotubes as a nanocatalyst for the Heck reaction

Heterogeneous Pd nanocatalysts are efficient catalysts for the Heck reaction but require multi-step,sophisticated procedures and harsh reaction conditions.In this work,a green and facile strategy has been developed to decorate Pd nanoparticles on polydopamine(PDA)-coated multi-walled carbon nano-tubes(Pd/CNTs-PDA)via a one-pot method.The obtained nanoparticles were characterized by various techniques including transmission electron microscopy,X-ray diffraction,and X-ray photoelectron spec-troscopy,which proved that Pd NPs are well-dispersed on the PDA and between the surfaces of the PDA and CNTs.The resultant Pd/CNTs-PDA catalysts exhibit excellent catalytic reactivity toward the Heck reaction at low temperatures.Moreover,by DFT simulation,we found that during the PDA polymeriza-tion process,a large number of unsaturated-N=and C=O species are more active than the groups on the PDA end product to anchor Pd NPs.The results provide evidence that the catalyst synthesized by the one-pot method exhibited good activity because sufficient active sites could be created to effectively promote Pd NPs dispersion during the dopamine polymerization process.Additionally,the Pd/CNTs-PDA catalyst was successfully employed in Heck cross-coupling reactions with various functionalized substrates.This method opens a window for the fabrication of high-performance nanocomposite catalysts under mild conditions using simple methods and has several potential applications.     

Synthesis and characterization of novel nanocomposite membrane of sodium titanate/Nafion

Novel nanocomposite membrane of sodium titanate/Nafion based on sodium titanate nanotubes with Nafion^® were prepared by solvent casting techniques. Nanotubes of sodium titanate were synthesized by hydrothermal method. TEM, XRD, and FTIR were employed to characterize the crystal phase, microstructure, and other physicochemical properties of the membrane and the nanotube samples. FTIR results showed us that the nanotube material of Na₂Ti₃O₇ has existed in the nanocomposite membrane of Na₂Ti₃O₇/Nafion. The existence of sodium titanate nanotubes in Nafion^® improves the methanol crossover and makes promising practical value of blocking methanol in direct methanol fuel cells.     

Hydrothermal processing of dye-adsorbing one-dimensional hydrogen titanate

One-dimensional hydrogen titanate consisting of mixed nanobelts, nanotubes, and nanorods have been processed via hydrothermal followed by high temperature calcination. The processed products have been characterized via transmission electron microscope, X-ray diffraction, spectrophotometer, spectrofluorometer, and Brunauer-Emmett-Teller surface-area measurement techniques for analyzing their morphology, structure, specific surface-area, band-gap, and photoluminescence. The dye-adsorption (in the dark) and photocatalytic activity (under ultraviolet-radiation exposure) of hydrothermally processed one-dimensional hydrogen titanate have been examined using methylene blue as a model catalytic dye agent. Under the present processing and test conditions, it is demonstrated that one-dimensional hydrogen titanate is a better dye-adsorbent than a photocatalyst due to its higher specific surface-area and relatively lower crystallinity.     

Synergistic effects of Mg-substitution and particle size of chicken eggshells on hydrothermal synthesis of biphasic calcium phosphate nanocrystals

Magnesium(Mg^2+))ion plays important roles in biomineralization of bone,teeth and calcium carbonate skeletons.Herein,chicken eggshells mainly comprising of Mg-calcite nanocrystals(Mg/(Mg+Ca)2.0 mol.%)were used to fabricate biphasic calcium phosphate(BCP),a mixture of hydroxyapatite(HA)and p-tricalcium phosphate(p-TCP)nanocrystals,through hydrothermal reactions at 200℃for 24 h.Our results indicated thatβ-TCP nanocrystals formed through the ion-exchange reactions of Mg-calcite,while HA nanocrystals were mainly produced by dissolution-reprecipitation reactions on the surfaces of eggshell samples in the hydrothermal system.Mg substitution in calcite resulted in formation ofβ-TCP nanocrystals instead of HA crystals through ion-exchange reactions.BCP samples with different compositions(28.6-77.8 wt.%β-TCP)were produced by controlling particle sizes of eggshells for hydrothermal reactions.The larger particles lead to the larger proportion ofβ-TCP in the BCP composition.Therefore,Mg substitution and particle size had synergetic effects on the hydrothermal synthesis of BCP using chicken eggshells through balance of ion-exchange and dissolution-reprecipitation reactions.Cell culture results showed that the BCP products were non-cytotoxic to MC3 T3-E1 cells,which may be used for bone substitute materials in future.     

Catalyst-free synthesis and characterization of boron nitride whiskers and nanotubes

Catalyst-free transformation of h-BN in an optical furnace in the flow of nitrogen results in formation of nanotubes, whiskers and negligible quantity of melted drops on the surface of heated samples. The thread-like structures and equiaxial particles were precipitated on a silicon substrate. The phase composition of the produced material is a mixture of h-BN, two boron-enriched tetragonal phases of BN (B_51,2N and B₂₅N), tetragonal and rhombohedric phases of pure boron and amorphous phase.An approximation of the spectral dependence of optical absorption versus photon energy of an incident light was explained in terms of absorption of the corresponding phases. Tetragonal phase of B_51,2N, tetragonal and rhombohedric phases of pure boron may correspond to band gap 3.5 eV, tetragonal phase of B₂₅N - 3.8 eV and hexagonal phase of BN - 4.8 eV. This fact confirms a theoretical assumption for the effect of boron excess in BN on a band gap.     

Microwave-assisted synthesis and characterization of cellulose-carbonated hydroxyapatite nanocomposites in NaOH-urea aqueous solution

We report the microwave-assisted synthesis of the cellulose-carbonated hydroxyapatite (CHA) nanocomposites with CHA nanostructures dispersed in the cellulose matrix by using the cellulose solution, CaCl₂, and NaH₂PO₄. The cellulose solution was previously prepared by the dissolution of microcrystalline cellulose in NaOH-urea aqueous solution. The influences of the heating time and cellulose concentration on the products were also investigated. The X-ray powder diffraction (XRD) and Fourier transform infrared spectrometry (FT-IR) results indicated that the obtained products were the cellulose-CHA nanocomposites. The scanning electron microscopy (SEM) micrographs showed the CHA nanostructures were dispersed in the cellulose matrix. The thermal stability of the cellulose-CHA nanocomposites in air was investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). This method is simple, fast, low-cost and suitable for large-scale production of cellulose-based nanocomposites.     

Large-scale synthesis and characterization of fan-shaped rutile TiO2 nanostructures

Large-scale fan-shaped rutile TiO₂ nanostructures have been synthesized by means of a simple hydrothermal method using only TiCl₄ as titanium source and chloroform/water as solvents. The physicochemical features of the fan-shaped TiO₂ nanostructures are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), nitrogen absorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy (UV-vis) and Fourier transform infrared spectroscopy (FTIR). Structural characterization indicates that the fan-shaped TiO₂ nanostructures are composed of several TiO₂ nanorods with diameters of about 5 nm and lengths of 300-350 nm. The average pore size and BET surface area of the fan-shaped TiO₂ nanostructures are 6.2 nm and 59 m²/g, respectively. Optical adsorption investigation shows that the fan-shaped TiO₂ nanostructures possess optical band gap energy of 3.11 eV.     

Studies on transformation of titanate nanotubes into nanoribbons

High aspect ratio titanate nanostructures were synthesized by simple hydrothermal treatment and the nature of two distinct morphologies, hollow nanotubes and titanate nanoribbons was explored as a function of hydrothermal processing conditions. The samples were characterized by means of SEM, XRD and TEM. The specific surface area of the final products was determined by Brunauer-Emmett-Teller (BET) method. It has been found that hydrothermal temperature and the treatment duration have a strong effect on the morphological control of the resulting products. Transformation of nanotubes into nanoribbons was observed with increase in the treatment temperature from 180 °C to 200 °C which became more dense with further increase in the temperature from 200 °C to 220 °C and treatment duration from 12 h to 24 h.     

Hydrothermal synthesis of titanate nanowire arrays

A simple templateless synthesis strategy for titanate nanowire arrays was developed by employing hydrothermal reactions. Hydrothermal treatment of metallic titanium powder with H₂O₂ in a 10 M NaOH solution produced a new sodium titanate compound, Na₂Ti₆O₁₃·xH₂O (x ∼ 4.2), as arrays of nanowires of lengths up to 1 mm. The nanowires were characterized by using XRD, SEM, TGA, and TEM. The nanowires have exceptionally large aspect ratios of 5000 or higher, and they can form arrays over a large area of 2 × 3 cm². Investigations on the reaction products in varied conditions indicate that the array formation requires simultaneously controlled formation and crystal growth rates of the Na₂Ti₆O₁₃·xH₂O phase.     

Recent progress in the development and properties of novel metal matrix nanocomposites reinforced with carbon nanotubes and graphene nanosheets

One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel nanocomposites.     

Annealing of ZnS nanocrystals grown by colloidal synthesis

ZnS nanocrystals (NCs) capped with tetramethylammonium (TMAH) were synthesized from ZnCl₂ · 2H₂O and thiourea using a wet chemical process. Further treatments of the nanocrystals such as aging, and annealing have been conducted to examine the stability of the grown samples. The X-ray diffraction spectra show that the crystal has a zinc blende structure with particle size of about 2 nm. The evidence of nanocrystalline character is also clear in the UV–Vis absorption that shows an excitonic peak at about 236 nm (5.2 eV) arising from band edge transitions. A photoluminescence emission peak centered at about 450 nm (2.7 eV) is attributed to transitions between shallow donors and Zn⁺ vacancies. Both absorption and photoluminescence spectra show that sample aging does not affect the characteristics of the sample, possibly due to protection by TMAH capping. Annealing at 700 °C and 900 °C results in the red shift of the photoluminescence.     

Low temperature synthesis and electrical characterization of germanium doped Ti-based nanocrystals for nonvolatile memory

Chemical and electrical characteristics of Ti-based nanocrystals containing germanium, fabricated by annealing the co-sputtered thin film with titanium silicide and germanium targets, were demonstrated for low temperature applications of nonvolatile memory. Formation and composition characteristics of nanocrystals (NCs) at various annealing temperatures were examined by transmission electron microscopy and X-ray photon-emission spectroscopy, respectively. It was observed that the addition of germanium (Ge) significantly reduces the proposed thermal budget necessary for Ti-based NC formation due to the rise of morphological instability and agglomeration properties during annealing. NC structures formed after annealing at 500 °C, and separated well at 600 °C annealing. However, it was also observed that significant thermal desorption of Ge atoms occurs at 600 °C due to the sublimation of formatted GeO phase and results in a serious decrease of memory window. Therefore, an approach to effectively restrain Ge thermal desorption is proposed by encapsulating the Ti-based trapping layer with a thick silicon oxide layer before 600 °C annealing. The electrical characteristics of data retention in the sample with the 600 °C annealing exhibited better performance than the 500 °C-annealed sample, a result associated with the better separation and better crystallization of the NC structures.     

Mechanochemical processing and microstructural characterization of pure Fe2B nanocrystals

The results of current investigation demonstrate that mechanochemical processing can be used to synthesize high purity Fe₂B nanocrystals by selecting well-optimized milling conditions, reaction paths and proper starting materials. Microstructure, phase analyses, specific surface area, and magnetic properties of the synthesized nanocrystals were examined by using X-ray diffraction/spectroscopy, electron microscopy, nitrogen adsorption–desorption methods following Brunauer-Emmett-Teller equation and vibrating sample magnetometer techniques, respectively. Removal of MgO impurity phase by leaching the resulting powder in the acetic acid solution yielded single phase Fe₂B nanocrystals with the crystallite size and specific surface area of 12.5 nm and 29 m²/g, respectively. Magnetization results clearly indicated the ferromagnetic behavior of Fe₂B nanocrystals with saturation magnetization observed around 96.26 emu·g^?1. Electron microscope images revealed coaxial/spherical powder shape and morphology of the single-phase Fe₂B nanocrystals.     

Novel multifunctional nanocomposites from titanate nanosheets and semiconductor quantum dots

A novel synthesis for a titanate nanosheets loaded nanocomposite has been developed. On this basis, a multifunctional material for optical applications has been fabricated with tunable refractive index, improved processing behavior and luminescent properties imparted by the incorporation of semiconductor quantum dots.Titanate synthesis, host material choice and quantum dots functionalization have been here addressed to obtain films with good optical quality and stable photoluminescence.In order to assess the potential application of the obtained nanocomposites, imprinting lithography and aerosol-based deposition techniques have been applied with promising results.The obtained nanocomposites have been characterized by UV–Vis, photoluminescence and FT-IR spectroscopy, X-ray diffraction and Transmission Electron Microscopy. The optical properties of the nanocomposite film have been tested by spectroscopic ellipsometry and M-line technique.     

Preparation,physical characterization and pharmacokinetic study of paclitaxel nanocrystals

Paclitaxel (PTX) is a natural broad-spectrum anticancer drug with poor aqueous solubility. PTX nanocrystals were formulated to improve the water solubility, and PTX nanosuspensions were prepared using anti-solvent precipitation, and then organic solvent and surfactants were removed by filtering through a vacuum system. The physical characterization of PTX nanocrystals were measured by transmission electron microscope, X-ray diffraction and differential scanning calorimetry. In addition, saturation solubility, in vitro release, stability and pharmacokinetic characteristics were examined. The average particle size of PTX nanocrystals was ～200?nm, and they had a stable potential and a uniform distribution. Paclitaxel nanocrystals can effectively improve drug solubility and in vitro release. PTX pharmacokinetic and tissue distribution studies were compared after intravenous administration of nanocrystals versus a commercial injection formulation. PTX nanocrystals were rapidly distributed with a longer elimination phase. Moreover, tissue distribution indicated that PTX nanocrystals are mainly absorbed by the liver and spleen and may offer reduced renal and cardiovascular toxicity which may reduce side effects.