Kezheng Chen

Facile synthesis of flower-like 3D ZnO superstructures via solution route

A novel flower-like 3D ZnO superstructure with high uniformity was fabricated on a large scale through a facile aqueous solution route at room temperature. The as-prepared ZnO superstructures with a diameter of about 3 μm are assembled by large amounts of interleaving nanosheets, which have a uniform thickness of about 15 nm and a well-crystalline structure with {100} planes as basal facets. The hierarchical microstructures, which were formed via a two-stage nucleation–growth process, highly depend on the concentration of NaOH and trisodium citrate dihydrate. The photoluminescence result indicates that the ZnO superstructures possess a relatively strong UV emission. The photodecomposition of methyl orange indicates that such ZnO superstructures possess excellent photocatalytic activity.

Synthesis and characterization of bifunctional magnetic–optical Fe3O4@SiO2@Y2O3 : Yb3+,Er3+ near-infrared-to-visible up-conversion nanoparticles

Bifunctional magnetic–optical Fe3O4@SiO2@Y2O3u2006:u2006Yb3+,Er3+ near-infrared-to-visible up-conversion nanoparticles (UCNPs) with core–shell structures have been successfully fabricated by a facile layer-by-layer method. The presented materials were characterized by XRD, FTIR, TEM, fluorescence spectrophotometer, NMR Analyzer and SQUID MPMS. The results showed that the Fe3O4 cores were uniformly coated by SiO2 and Y2O3u2006:u2006Yb3+,Er3+ layers. The amorphous silica used as the transition layer of UCNPs played an essential role in directing the structure of the composites. The inner Fe3O4 cores and the outer Y2O3u2006:u2006Yb3+,Er3+ layers endow the composites with robust magnetic responsive properties and strong up-conversion fluorescent properties, which endow the nanoparticles with great potential applications in drug targeting, bioseparation and diagnostic analysis.

Nano-scaled hierarchical porous ZnO nanostructures: fabrication and application in dye-sensitized solar cells

Three-dimensional (3D) hierarchical porous ZnO architectures constructed by sheet-like structures were prepared through calcination of a bilamellar basic zinc citrate intermediate. The molar ratio of citrate anion/Zn2+ and the pH value of the reaction solution play crucial roles in the formation of the 3D hierarchical nanostructures. On the basis of the synthetic experimental results, a growth mechanism is proposed in the case of citrate as the organic ligand. The resulting nano-scaled porous ZnO structures exhibit a high specific surface area up to 55.6 m2 g−1 with a pore size of 5.1 nm. A light-to-electricity conversion efficiency of 4.46% was achieved of the dye-sensitized solar cells with the porous ZnO as the photoanode.

Controlled synthesis and enhanced luminescence of europium-doped fluorine-substituted hydroxyapatite nanoparticles

Europium-doped fluorine-substituted hydroxyapatite (Eu:FHAp) nanoparticles with different morphologies were synthesized by a simple hydrothermal method. The structure, composition, morphology, and luminescence of the products were investigated by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. The prepared Eu:FHAp had a nanorod-like shape and their aspect ratios dropped when the pH of the solution was increased from 3.0 to 11.0. The luminescence intensity of the products increased significantly with increasing substitution of OH− with F−. The nanoparticles did not adversely affect the growth of hela cells, which indicates that they have potential applications as fluorescent cell labeling agents.

One-pot and template-free fabrication of dendritic and octahedral single-crystal magnetites†

Dendritic and octahedral single-crystal magnetites have been successfully fabricated by a facile one-pot hydrothermal method without any templates. The presented materials were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), selection area electron diffraction (SAED) and magnetic property measurement system (MPMS). The results showed that the prepared magnetites with different morphologies have face-centred cubic structures. When using different amounts of potassium hydroxide (KOH) and hydrazine hydrate (N2H4·H2O), high yields of Fe3O4 with well-defined three-dimensional (3D) dendritic and octahedral shapes were obtained. Moreover, the reaction time also has an important effect on the shapes of the products. The crystal growth directions of dendritic and octahedral magnetites are oriented along [110] and [111], respectively. The formation mechanism of the magnetites with different morphologies has been discussed. The magnetic properties are closely related to the morphologies of the magnetites. Furthermore, the as-prepared products have a high saturation magnetization and low coercive force, which endow the materials with great potential for applications in biological fields.

Hundreds of milligrams of Cr(VI) adsorbed on each gram of Cu2O@Cu fractal structures: kinetics, equilibrium, and thermodynamics

In this study, branch-like Cu2O@Cu fractal structures were prepared by a facile urea-assisted solvothermal procedure. Each branch of the fractal had its own branch and outstretched along a direction of 60°. On the basis of the Langmuir isotherm model, the maximum Cr(VI) adsorptive capacities on these fractal structures were estimated to be 360, 520, 460, and 760 mg g−1 at 293, 298, 303, and 308 K, respectively. These values, to our knowledge, were much larger than those reported for metal oxide adsorbents in previous literature. More strikingly, with the help of a pseudo-second-order model, the initial Cr(VI) adsorption rate was estimated to be 32 mg g−1 min−1, which was significantly higher than those reported for many other adsorbents. Thermodynamic analyses of enthalpy, entropy and Gibbs free energy further demonstrated that these outstanding kinetics and equilibrium results were mainly due to a spontaneous quasi-chemical adsorption process, rather than the impacts of the specific surface area and volume density of our fractal adsorbents.

Hydrothermal synthesis of microstructured fluoridated hydroxyapatite coating on magnesium alloy

Fluoridated hydroxyapatite (FHAp) coating was directly fabricated on AZ91D magnesium alloy without using any chelating agents by a facile hydrothermal method. The results show that the as-prepared coating is mainly composed of FHAp and magnesium whitlockite. The morphology of the FHAp coating is changed with the increase of the F− ion doping amount, and the FHAp-0.04 coating has a much uniform and dense structure than the FHAp-0.02 coating. The FHAp coating can remarkably reduce the corrosion rate of the substrate in simulated body fluid (SBF) solution, particularly during the initial immersion stages. Moreover, the FHAp coating can also induce the formation of apatite particles after being immersed in SBF, indicating the good bioactivity of the coating.

Novel synthesis of AB-type carbonated hydroxyapatite hierarchical microstructures with sustained drug delivery properties

In this study, AB-type carbonated hydroxyapatite (CHAp) nanosheet-assembled hollow microstructures were rapidly synthesized via a hydrothermal process without sintering. Urea was employed as both a pH adjusting agent and a CO32− source during hydrothermal reaction. The influence of hydrothermal time on the final morphologies of the products was systematically investigated. The as-prepared CHAp hollow microstructures with a diameter of about 3–4 μm consist of numerous radially oriented CHAp nanosheets as building units with an average thickness of about 10 nm. The morphology of the product can vary from a hollow microstructure to a solid dandelion-like structure with increasing hydrothermal time. Possible mechanisms for the formation of a nanosheet-assembled CHAp hollow microstructure and a solid dandelion-like microstructure in the presence of both urea and ethylenediaminetetraacetic acid (EDTA) are illustrated. Moreover, the as-prepared CHAp hollow microstructures exhibit a high drug loading capacity and sustained drug release properties.

Preparation and electrical characterization of carbon nanotube /ZrO2 composite ceramics

Carbon nanotubes (CNTs) in a kind of ideal reinforcements for structural materials, as well as the promising components to prepare multifunctional composites. In this paper, multi-walled carbon nanotube /ZrO2 functional composite ceramics were investigated and successfully fabricated via the spark plasma sintering technique. The structures of nanocomposite ceramics were characterized by XRD, SEM and EDS, and their mechanical and electrical properties were also studied. It was found that there is an increasing of 18% in ceramics toughness compared with pure ZrO2 ceramics prepared by the same method. Interestingly, the results of the AC complex impedance spectra at 25~325 °C showed that the electrical resistance of the ceramics increased with the temperature under 150 °C, and will decrease dramatically when it is higher than 150 °C.

A facile, versatile approach to hydroxyl-anchored metal oxides with high Cr(VI) adsorption performance in water treatment

In this study, a facile and versatile urea-assisted approach was proposed to synthesize Chinese rose-like NiO, pinecone-like ZnO and sponge-like CoO adsorbents. The presence of urea during syntheses endowed these adsorbents with high concentration of surface hydroxyl groups, which was estimated as 1.83, 1.32 and 4.19u2009mmolu2009[OH−]u2009g−1 for NiO, ZnO and CoO adsorbents, respectively. These surface hydroxyl groups would facilitate the adsorption of Cr(vi) species (e.g. HCrO4−, Cr2O72− and CrO42−) from wastewater by exchanging with hydroxyl protons or hydroxide ions, and hence result in extremely high maximum adsorbed amounts of Cr(vi), being 2974, 14u2009256 and 408u2009mgu2009g−1 for NiO, ZnO and CoO adsorbents in the pH range of 5.02–5.66 at 298u2009K, respectively. More strikingly, the maximum adsorbed amounts of Cr(vi) would be greatly enhanced as the adsorbing temperature is increased, and even amount to 23u2009411u2009mgu2009g−1 for ZnO adsorbents at 323u2009K. Based on the kinetics and equilibrium studies of adsorptive removal of Cr(vi) from wastewater, our synthetic route will greatly improve the adsorptivity of the as-synthesized metal-oxide adsorbents, and hence it will shed new light on the development of high-performance adsorbents.