Haijiao Zhang

Nanosized zinc oxide particles induce neural stem cell apoptosis

Given the intensive application of nanoscale zinc oxide (ZnO) materials in our life, growing concerns have arisen about its unintentional health and environmental impacts. In this study, the neurotoxicity of different sized ZnO nanoparticles in mouse neural stem cells (NSCs) was investigated. A cell viability assay indicated that ZnO nanoparticles manifested dose-dependent, but no size-dependent toxic effects on NSCs. Apoptotic cells were observed and analyzed by confocal microscopy, transmission electron microscopy examination, and flow cytometry. All the results support the viewpoint that the ZnO nanoparticle toxicity comes from the dissolved Zn(2+) in the culture medium or inside cells. Our results highlight the need for caution during the use and disposal of ZnO manufactured nanomaterials to prevent the unintended environmental and health impacts.

Monolayer graphene/NiO nanosheets with two-dimension structure for supercapacitors

In this paper, graphene oxide (GO) synthesized from the modified Hummer method is used directly to fabricate unique two-dimension graphene/NiO composite material. Nickel ions are adsorbed on both sides of GO based on self-assembly by the electrostatic interactions of two species, forming the monolayer graphene/NiO sheet. The as-prepared composite is characterized using X-ray diffraction (XRD), Raman, SEM, TEM, Energy Dispersive Spectrometer (EDS) analysis and nitrogen adsorption/desorption. The results demonstrate that the NiO nanoparticles (5–7 nm) is uniformly dispersed on the surface of graphene, which greatly increases the surface area of the composite (134.5 m2 g−1). This two-dimensional structure enhances supercapacitive performance with a high specific capacitance of 525 F g−1 at a current density of 200 mA g−1. A capacity retention of 95.4% can be maintained after 1000 cycles, suggesting its promising potential in supercapacitors.

Self-assembly fabrication of 3D flower-like ZnO hierarchical nanostructures and their gas sensing properties

In this paper, three-dimensional flower-like ZnO hierarchical nanostructures were fabricated from the thermal-decomposition of 3D zinc hydroxide carbonate precursor, which was synthesized by a urea hydrothermal method with block copolymer F127 (EO106-PO70-EO106) as the morphology director. XRD, IR, UV-vis, SEM, TEM, TG and N2 adsorption–desorption isotherms have been employed to characterize the products. The influences of synthesis parameters such as reaction time, the type of zinc sources, and species concentration on the morphologies of the products were systematically studied. It was found that the reaction time played a key role in determining the final morphology of porous ZnO. On the basis of experimental results, a possible formation mechanism of the 3D flower-like ZnO hierarchical nanostructures was discussed. More importantly, the gas sensing tests indicated that the sensor made from porous ZnO hierarchical nanostructures exhibited better gas sensing properties to n-butanol compared with the sensor based on the commercial ZnO nanoparticles. The enhancement in gas sensing properties was attributed to their unique 3D hierarchical nanostructures, high surface areas, and greater number of surface active sites.

Surfactant-free solution phase synthesis of monodispersed SnO2 hierarchical nanostructures and gas sensing properties

In this work, SnO2 hierarchical nanostructures were successfully prepared via a simple and surfactant-free hydrothermal process starting from stannous sulfate (SnSO4) and trisodium citrate dihydrate (Na3C6H5O7·2H2O) in a suitable ethanol–water system. TEM and HRTEM images showed that the obtained SnO2 products are uniform, well-dispersed, and have spherical architectures, composed of tiny primary nanocrystals, and the diameters are about 50 nm. It was found that the amount of Na3C6H5O7·2H2O and the volume ratio of ethanol and water played important roles in determining the final morphologies of the products. The gas sensing results indicated that the sensor made from porous SnO2 nanostructures calcined at 400 °C exhibited excellent gas sensing performance to butanol at the low temperature compared with those under higher calcination temperature and commercial SnO2. The SnO2 hierarchical nanostructures possess uniform size and large surface areas, making them ideal candidates for more potential applications such as battery electrodes and as opto-electronic devices.

Porous TiO2 hollow nanospheres: synthesis, characterization and enhanced photocatalytic properties

A facile solvothermal process combined with a precursor thermal transformation method has been developed for preparing porous TiO2 hollow nanospheres with a high surface area and a good thermal stability. The porous TiO2 hollow spheres were obtained by using TiOSO4 as a titanium source and carbon nanospheres as a sacrificial template. Their particle size, diameter and morphology can be readily controlled by varying growth parameters, including reaction temperature, time and reagent concentration. The calcination temperature of TiO2–C core-shell nanospheres was found to have a profound effect on the structure and properties of the final products. The photocatalytic activities of the products were evaluated by the photodegradation of methyl orange (MO). The TiO2 hollow spheres obtained from 450 °C thermal treatment exhibited higher photocatalytic activity than commercial Degussa P25 in the presence of Cr(VI). The possible photodegradation mechanism was also investigated.

Preparation of flower-like ZnO architectures assembled with nanosheets for enhanced photocatalytic activity.

As an important semiconductor metal oxide, various methods have been developed for preparation of ZnO architectures owing to their excellent properties and extensive applications. In this paper, two kinds of 3D flower-like ZnO architectures assembled with numerous nanosheets were successfully synthesized by a simple hydrothermal route assisted by sodium dodecyl sulfate (SDS), origining from the different alkali environment created by urea and hexamine (HMT). SEM and TEM results revealed that the two products had hydrangea-like and rose-like nanostructures with uniform particle sizes, respectively. XRD results confirmed that the growth process of ZnO involved a phase transformation from intermediate compound basic zinc carbonate to ZnO. Base on the experimental results, the formation mechanisms of two kinds of flower-like ZnO undergoing nucleation, oriented growth and self-assembly processes were discussed. The photocatalytic results indicated that both samples exhibited high photocatalytic activities and good cycling stability for the degradation of rhodamine B (RhB), which was almost completely degraded within 25min, in comparison to those milled samples (above 45min). The excellent performances were mainly ascribed to their unique nanostructure, good stability, and uniform particle size.

A soft–hard template approach towards hollow mesoporous silica nanoparticles with rough surfaces for controlled drug delivery and protein adsorption

In this work, a novel type of hollow mesoporous silica nanoparticle (HMSN) with a rough surface has been successfully prepared via a facile soft-hard template route by using a carbon nanosphere as a hard template and cetyltrimethylammonium bromide (CTAB) as a soft template, respectively. This method involves the preparation of a carbon nanosphere, sequential coating of double SiO2 layers, and the removal of the inner carbon core and CTAB to produce HMSNs. The obtained HMSNs possess spherical morphology, a mesoporous shell, and crumpled surfaces. The controlled experiments prove that the addition of 3-ammonia propyl triethoxy silane (APTES) is very crucial for the formation of desired HMSNs. The cell tests indicate that HMSNs show a good biocompatibility. As a result, the potential applications of HMSNs are further explored for drug delivery and protein adsorption, using doxorubicin hydrochloride (DOX) and Cytochrome c (Cyt c) as the model drug and protein, respectively. The HMSNs exhibit high drug loading and protein adsorption capacity, as well as the controlled pH-responsive release behavior for DOX. Therefore, the HMSNs prepared are ideal candidates for various applications such as nanoreactors, drug delivery and protein adsorption.

Self-assembly and template-free synthesis of ZnO hierarchical nanostructures and their photocatalytic properties

Despite significant progress in the field of semiconductor photocatalysis has been made, it is still a great challenge to prepare low-cost photocatalysts with high activities. In our work, three dimensional (3D) flower-like ZnO hierarchical nanostructures assembled with numerous nanosheets were fabricated by a simple, template-free and one-step hydrothermal route. The products were characterized by XRD, UV-Vis, PL, SEM, TEM, HRTEM techniques. In the process, NH4F played a crucial role for the formation of ZnO hierarchical nanostructures, which was acted both as the alkali source and morphology director. Furthermore, the growth of ZnO involved a phase transformation from intermediate compound ZnF(OH) to ZnO. To further improve the photocatalytic activity, Ag-doped ZnO photocatalyst was also prepared. The photocatalytic results indicated that the Ag/ZnO exhibited higher photocatalytic activity than the pure ZnO. The great enhancement was mainly ascribed to their unique hierarchical nanostructures as well as the modification of Ag nanoparticles. Additionally, both ZnO and Ag/ZnO microspheres showed good recycling stabilities over several separation cycles in photodegradation.

A facile route for rapid synthesis of hollow mesoporous silica nanoparticles as pH-responsive delivery carrier.

In this paper, a facile and effective route has been developed for rapid synthesis of hollow mesoporous silica nanoparticles (HMSNs) by using tetradecyltrimethylammonium bromide (TTAB) as the porogen with the assistance of triethanolamine (TEA). The products were characterized by various techniques including TEM, SEM, BET, and FT-IR, etc. The HMSNs obtained possess spherical morphology, mesoporous channels and very high specific surface areas (1355m(2)g(-1)). According to the experimental results, a possible formation mechanism was discussed. Moreover, the ability of HMSNs as drug carrier was evaluated by selecting doxorubicin hydrochloride (DOX) as the model drug. The results indicated that HMSNs showed high loading capacity and controlled pH-responsive release behavior. Considering their unique nanostructures and porous properties, we expect the HMSNs prepared have more potential applications in various fields such as nanoreactors, cellular imaging, and biosensor.

Smart and flexible supercapacitor based on a porous carbon nanotube film and polyaniline hydrogel

Smart and flexible supercapacitors are of ever increasing importance for energy-storage devices. Herein, a simple and effective strategy to make a supercapacitor in a “flexible” and “electrochromic” way was based on the direct and convenient immobilization of a polyaniline (PANI) hydrogel onto a porous carbon nanotube (CNT) film. The resultant symmetric all-solid-state supercapacitor showed a favorable specific capacitance of 315 F g−1 and a relatively high cycling stability (92% capacitance retention after 1500 cycles). The bending test indicated that the obtained supercapacitor was flexible and its performance was only decreased by less than 7.0% after 150 bending cycles with a bending angle of 180°. Furthermore, the supercapacitor displayed a rapid and reversible chromatic transition between different working stages, and its level of stored energy could be quickly determined by the naked eye in a predictable and noticeable manner. This work may open a simple and convenient avenue for the fabrication of smart, flexible and all-solid-state supercapacitors.